Rail transportation is considered in thissection as a system in which vehiclesare supported and guided by rails orother guideways. Rail-transportation
engineering deals with the need, planning, selec-tion, design, and construction of such systems formovement of passengers and freight. It involvesroadbed, track, bridges, trestles, culverts, yards,terminals, stations, office buildings, locomotivefueling facilities, environmental protection facili-ties, signals and communications, track-side pro-tection devices, and railroad-car, locomotive, andtransit-vehicle maintenance facilities. Engineersmay be responsible for maintenance of way andstructures. And they must be familiar with motivepower, railway cars, and other equipment.
Rail transportation is the most effective way tohandle increased transportation demands withrelatively low power requirements, a low landrequirement, little air pollution, and few accidentsinvolving fatalities and injuries. As a result, aspopulation and gross national product increase,rail transportation increases in importance. TheU.S. Congress, in recognition of this, has passedlegislation that, in particular, has added to theimportance of rail transportation of freight andof passenger rail transit, for example, throughderegulation under the Staggers Act in the early1980s and the Intermodal Surface Transportation
Efficiency Act (ISTEA) about a decade later. In1998, Congress passed the Transportation EquityAct for the 21st Century (TEA-21). A portion of thislaw authorizes Federal funding for grade crossingsafety, transit and high speed rail systems andadditional research on magnetic levitation tech-nology. Additional legislation is being consideredto fund development of viable high speed railcorridors.
19.1 Glossary
Following are terms commonly encountered in rail-transportation engineering:
Alignment. Horizontal location of a railroad asdescribed by tangents and curves.
Apron, Car Ferry. Bridge structure supportingtracks and connecting the car deck of a car ferry toland. The apron is hinged at the shore end so that itis free to move vertically at the outboard end toaccommodate varying elevations of the ferry.
Apron, Track. Railroad track along the waterfrontedge of a pier or wharf for direct transfer of cargobetween ship and car.
Ballast. Selected material, such as crushed stone,placed on the roadbed to hold the track in line andsurface.
Batter Rail. The deformation of the surface of thehead of a rail at the end.
Batter (Pile). Slope of inclined piles.*Updated and revised from Sec. 19, Rail-Transportation
Engineering, by D.L. McCammon in the fourth edition.
Any use is subject to the Terms of Use as given at the website.
Source: Standard Handbook for Civil Engineers
Branch Line. Secondary line or lines of a railway.
Branding. Identification markings hot-rolled inraised figures and letters on a rail web indicatingweight of rail and section number, type of rail, kindof steel, name of manufacturer and mill, and yearand month rolled.
Car, Light Rall (Trolley Car). A self-propelledvehicle operating on rails, generally in streets, anddrawing electric power from overhead or under-ground conductors.
Car, Motor. A powered track car for transportingtwo to six people.
Car, Push. A four-wheeled railway work cardesigned to be pushed by hand or towed by amotorcar. It is used to transport materials tooheavy to be carried on a motorcar.
Car, Track. Any car or machine operated ontrack, such as a motorcar, handcar, or trailer.
Car Retarder. Braking device, usually power-operated, built into a railway track to reduce thespeed of cars. Brake shoes, when set in brakingposition, press against the sides of the lower por-tion of the car wheels.
Compromise Joint. Joint bars for connecting railsof different fishing height and section, or rails of thesame section but with different joint drillings.
Cradle. Structure riding on an inclined track on ariverbank and having a horizontal deck with atrack on it for transfer of railroad cars to and fromboats at different water elevations.
Crib. Space between two successive ties.
Crossing, Grade. An at-grade crossing of a rail-road and a highway, usually with protective de-vices such as warning signs, flashing lights, bells orgates.
Crossing (Track). Construction used where onetrack crosses another at grade; it consists of fourconnected frogs.
Crossing, Bolted Rail. A crossing in which all therunning surfaces are of rolled rail. The parts areheld together with bolts.
Crossing, Manganese-Steel Insert. A crossing inwhich a manganese-steel casting is inserted at eachof the four intersections. Fitted into rolled rails, thecasting forms the points and wings of the crossingfrogs.
Crossing, Solid Manganese-Steel. A crossing inwhich the frogs are of the solidmanganese-steel type.
Crossing, Movable-Point. A crossing of smallangle in which each of the two center frogs con-sists essentially of a knuckle rail and two opposedmovable center points with the necessary fixtures.
Crossing, Single-Rail. A crossing in which theconnections between the end frogs and the centerfrogs consist of running rails only.
Crossing, Two-Rail. A crossing in which the con-nections between the end frogs and the center frogsconsist of running rails and guardrails.
Crossing, Three-Rail.A crossing inwhich the con-nections between the end frogs and the center frogsconsist of running rails, guardrails, and easer rails.
Crossing Plates. Plates interposed between acrossing and the ties or other timbers to protectthe ties and to support the crossing better by dis-tributing loads over larger areas.
Crossover. Two turnouts with the track betweenthe frogs arranged to form a continuous passagebetween two nearby and generally parallel tracks(Fig. 19.15).
Crossover, Double. Two crossovers that intersectbetween the connected tracks; also two crossoverswithin a short distance that allow movements toconnected tracks.
Curve, Compound. A continuous change in align-ment effected with two or more contiguous, simplecurves of different radii but with a common tan-gent at each junction (Fig. 19.5).
Curve, Degree of. (See Degree of Curve.)
Curve, Easement. A curve whose radius varies toprovide gradual transition between a tangent anda simple curve or between two simple curves ofdifferent radii (Fig. 19.7).
Curve, Lead. Curve between switch and frog in aturnout (Fig. 19.15).
Curve, Reverse. Curve formed by two contigu-ous, simple curves with a common tangent butwith centers of curvature on opposite sides of thetangent (Fig. 19.6).
Curve, Simple.A continuous change in alignmenteffected with an arc of constant radius and fixedcenter (Fig. 19.4).
Degree of Curve.Angle subtended at the center ofa simple curve by a 100-ft chord.
Derail. A track structure for derailing rollingstock in an emergency.
Easer. (See Rail, Easer.)
Elevation of Curves (Superelevation). Height ofouter rail above inner rail along a curve.
Fishing Space. Space between head and base of arail occupied by a joint bar (Fig. 19.13).
Flangeway. Open way through a track structurethat provides a passageway for wheel flanges (Fig.19.16).
Flare. A tapered widening of the flangeway atthe end of a guard line of a track structure. A flaremay be at the end of a guardrail or at the end of afrog or crossing wing rail (Fig. 19.16).
Foot Guard. Filler for space between convergingrails to prevent a foot from being accidentallywedged between the rails.
Frog. A track structure at the intersection of tworunning rails to provide support for wheels andpassageways for their flanges, thus permittingwheels on either rail to cross the other (Fig. 19.16).
Frog Angle. The angle formed by the intersectinggage lines of a frog.
Frog, Bolted Rigid.A frog built of rolled rails withfillers between, held together with bolts.
Frog, Center. Either of the two frogs at the oppo-site ends of the short diagonal of a crossing.
Frog, End. Either of the two frogs at the oppositeends of the long diagonal of a crossing.
Frog, Flange. (See Frog, Self-Guarded.)
Frog, Heel of. The end of the frog farthest fromthe switch.
Frog, Movable Point.A frog with a movable pointto eliminate the flangeway gap in locations withsmall frog angles.
Frog Number. Half the cotangent of half the frogangle.
Frog Point. That part of a frog lying between theextensions of the gage lines from their intersection
toward the heel end (part farthest from the switch).The theoretical point is the intersection of the gagelines. The half-inch point is located at a distancefrom the theoretical point toward the heel equal,in inches, to half the frog number and at whichthe spread between the gage lines is 1⁄2 in. Usually,measurements are made from the half-inch frogpoint.
Frog, Rail-Bound Manganese-Steel. A frog con-sisting essentially of a manganese-steel body cast-ing fitted into and between rolled rails and heldtogether with bolts (Fig. 19.16a).
Frog, Self-Guarded (Flange Frog). A frog withguides or flanges above its running surface to con-tact the tread rims of wheels to guide their flangessafely past the point of the frog (Fig. 19.16b).
Frog, Solid Manganese-Steel. A frog consistingessentially of a single manganese-steel casting (Fig.19.16b).
Frog, Spring-Rail. A frog with a movable wingrail normally held against the point rail by springs.The rails thus form an unbroken running surfacefor wheels on one track, whereas the flanges ofthe wheels on the other track force the movablewing rail away from the point rail to provide apassageway. Viewed from the toe end toward thepoint, a right-hand frog has the movable wing railon the right-hand side.
Frog, Toe of. The end of the frog closest to theswitch.
Gage (Track). Distance between gage lines (Fig.19.9). (Standard gage is 4 ft 81⁄2 in.)
Gage (Track Tool). A device by which the gage ofa track is established or measured.
Gage Line.A line 5⁄8 in below the top of the centerline of head of running rail or corresponding loca-tion of tread portion of other track structures alongthat side nearer the center of track.
Grade Line. Line on profile representing tops ofembankments and bottoms of cuts ready to receiveballast. This line is the intersection of the plane ofthe roadbed with a vertical plane through thecenter line.
Guard, Stock. A barrier between and along trackrails to prevent passage of livestock on or along thetrack.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Guard Check Gage. Distance between guard andgage lines, measured perpendicular to gage linesacross the track.
Guard Face Gage. Distance between guard lines,measured perpendicular to gage line across thetrack.
Guard Line. A line along that side of the flang-eway nearer the center of track and at the same ele-vation as the gage line.
Guard Timber. A longitudinal timber placedoutside the track rail to maintain tie spacing.
Guardrail. A rail or other structure parallel to therunning rails of a track used to prevent wheelsfrom being derailed, or to hold wheels in correctalignment to prevent their flanges from striking thepoints of turnouts, crossing frogs, or switches.Also, a guardrail is a rail or other structure laidparallel to the running rails of a track to keepderailed wheels adjacent to running rails.
Guardrail, Frog. A rail or other device to guidea wheel flange so that it is kept clear of the point ofa frog.
Guardrail, Inner. A longitudinal member, usuallya metal rail, secured on top of the ties inside thetrack rail to guide derailed wheels.
Guardrail, One-Piece. A guardrail consisting of asingle component so designed that no auxiliaryparts or fastenings other than spikes are requiredfor its installation.
Hi-Rail Vehicle. A truck or other vehicle withspecial wheel assemblies that allow for travel ontrack in addition to highways.
Joint, Compromise. See Compromise Joint.
Joint, Insulated. A rail joint with insulatingmaterial to prevent the flow of electric currentbetween abutting rail ends.
Joint, Rail. Splice uniting abutting ends of con-tiguous rails.
Joint Bar. A stiff steel member commonly used(in pairs) to join rail ends and to hold them firmly,evenly, and accurately in surface and gage-sidealignment (Fig. 19.13).
Joint Gap. Distance between ends of contiguousrails in track, measured on the outside of the head5⁄8in below top of rail.
Lead. Distance between actual point of a switchand half-inch point of a frog. The actual lead ismeasured along the line of the parent track (Fig.19.15). The curved lead is measured to the half-inchpoint of the frog but along the outside gage line ofthe turnout. The theoretical lead is the distancefrom the theoretical point of a uniform turnoutcurve to the theoretical point of the frog, measuredalong the line of the parent track.
Nosing. A transverse, horizontal motion of alocomotive that exerts a lateral force on the sup-porting structure.
Out of Face (Trackwork). Work, such as tie re-placement, that proceeds completely and continu-ously over a given piece of track as distinguishedfrom work at disconnected points.
Rail (Track). A rolled steel shape, commonly a Tsection, laid end to end, on crossties or othersuitable supports, to form a track for railwayrolling stock (Fig. 19.10).
Rail, Closure. Rail between the parts of anyspecial trackwork layout, such as the rail betweenswitch and frog in a turnout (sometimes called leador connecting rail); also the rail connecting thefrogs of a crossing or of adjacent crossings but not apart of the crossings (Fig. 19.15).
Rail, Compromise. Relatively short rail with twoends of different section to correspond with theends of rails to be joined. It provides the transitionbetween rails of different section.
Rail, Easer. A rail that provides a bearing for theportion of hollowed-out treads of worn wheels thatoverhangs a running rail. Sloped at the ends, aneaser is laid with its head along the outside of andclose to the head of the running rail.
Rail, Guard. (See Guardrail.)
Rail, Knuckle. A bent rail or equivalent structureforming an obtuse point at a movable-pointcrossing or slip switch. When set for traffic, themovable points of the crossing or switch restagainst the obtuse point.
Rail, Reinforcing.A bent rail placed with its headoutside of and close to the head of a knuckle rail tostrengthen it and act as an easer rail; or a piece ofrail similarly applied to a movable center point.
Rail, Running. Rail or surface on which the treadof a wheel bears.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Rail, Stock. Running rail against which theswitch rail operates.
Rail, Switch (Switch Point or Switch-Point Rail).Tapered rail of a split switch (Fig. 19.17).
Rail, Welded. Two or more rails welded togetherto form a length less than 400 ft. When the length is400 ft or more, the result is called a continuouswelded rail.
Retarder, Car. See Car Retarder.
Retarder, Insert. A braking device without exter-nal power, built into a railway track to reduce thespeed of cars with brake shoes against the sides ofthe lower portions of wheels. Sometimes, meansare provided to open the retarder to nullify itsbraking effect.
Right-of-Way. Lands or rights used or held forrailroad operation.
Shoulder. That portion of the ballast between theend of the tie and the toe of the ballast slope.
Siding. Track, auxiliary to the main track, used topermit trains to pass.
Spot Board. A sighting board placed above andacross the track at a proposed elevation for therails to indicate the new surface and insure itsuniformity.
Stamping. Figures and letters indented, after hotsawing, in the center of the rail web, parallel withthe direction of rolling, to indicate the serial heatnumber, ingot number as cast or rolled, andposition of each rail relative to top of ingot.
Station, Loop.A form of through station in whichthe station track layout embraces a loop or part of acircle. Trains move in one direction only and turnrelative to the station.
Station, Stub. Station with tracks connected atone end only.
Station, Through. Station with tracks connectedat both ends.
Stock Pass. A culvert or bridge opening under atrack primarily for passage of livestock.
Subballast.Material of superior character spreadon the finished subgrade of a roadbed below thetop-ballast to provide good drainage, prevent frostupheaval, and distribute the load over the roadbed(Figs. 19.1 and 19.9).
Subgrade. Finished surface of roadbed belowballast and track.
Surface, Running (Tread). Top part of structureson which the treads of wheels bear.
Switch. A track structure for diverting rollingstock from one track to another (Fig. 19.17).
Switch Rod. The rod connecting to the switchstand to enable movement of the switch points.
Switch, Slip. A combination of a crossing withleft- and right-hand switches and curves betweenthemwithin the limits of the crossing connecting thetwo intersecting tracks on both sides of the crossingwithout separate turnout frogs. A single slip switchcombines a crossing with one right-hand and oneleft-hand switch; a double slip switch, with tworight-hand and two left-hand switches.
Switch, Split. A switch consisting essentially oftwo movable-point rails with necessary fixtures(Fig. 19.17).
Switch, Spring. A switch with an operatingmechanism incorporating a spring device to returnthe movable points automatically to their originalor normal position. This action takes place after thepoints have been shifted by the flanges of trailingwheels passing along the track other than that forwhich the points are set for facing movements.
Switch Angle. Angle between the gage lines of astock rail and the switch rail at its point.
Switch Detector Bar. Strip of metal, alongside thetrack rail, connected with the throwing mechanismof a switch to prevent moving of the switch undertrains.
Switch Heel. End of a switch rail nearer thefrog. Heel spread is distance at the heel betweengage lines of stock and switch rails (standardized at61⁄4in for straight switches).
Switch Point. (See also Rail, Switch.) Theore-tically, the intersection of the gage line of theswitch rail, extended, and the gage line of the stockrail. The actual point is that end of the switch railfarther from the frog; the point where thespread between the gage lines of stock and switchrails is sufficient for a practicable switch point(Fig. 19.17).
Switch Stand. Device for manual operation ofswitches or movable center points.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Switch Throw. Distance through which points ofswitch rails are moved sideways (standardized at43⁄4 in). It is measured along the center line of theNo. 1 switch rod or head rod.
Tangent. Straight rails or track; specifically,straight track contiguous with a curve.
Tie, Cross. The transverse member of the trackstructure to which rails are fastened to provideproper gage and to cushion and distribute trafficloads (Fig. 19.9). An adzed tie has plate-bearingareas on top made plane and smooth by machine. Abored tie has machine-made holes for spikes. Agrooved tie has depressions machine-gouged acrossits top into which ribs on the bottom of a tie plate fit.
Tie, Heartwood. A tie with sapwood no widerthan one-fourth the width of the tie top between 20and 40 in from midlength.
Tie, Sapwood. A tie with sapwood wider thanone-fourth the width of the tie top between 20 and40 in from midlength.
Tie, Slabbed (Pole Tie, Round Tie). A tie sawed onends, top, and bottom only.
Tie, Switch. A tie that functions as a crosstie butis longer and also supports a crossover or turnout.
Tie Plate. Plate interposed between a tie and railor other track structure (Fig. 19.9).
Topballast.Material of superior character spreadover a subballast to support the track structure,distribute the load, and provide good drainage(Fig. 19.1).
Track. Assembly of rails, ties, and fasteningsover which cars, locomotives, and trains move.
Track, Body. Each of the parallel tracks of a yardon which cars are moved or stored.
Track, Connecting. Two turnouts with the trackbetween the frogs arranged to form a continuouspassage between one track and another intersec-ting or oblique track or another remote, paralleltrack.
Track, Crossover. (See Crossover.)
Track, Drill. A track connecting with a laddertrack and over which locomotives and cars pass inswitching.
Track, House. A track alongside or entering afreight house and used for cars receiving or de-livering freight.
Track, Ladder. Track connecting the body tracksof a yard.
Track, Lead.An extended track connecting eitherend of a yard with the main track.
Track, Main. Track extending through yards andbetween stations and on which trains are operatedby timetable or train order, or both, or the use ofwhich is governed by block signals.
Track, Rider. A track in a hump yard on which aconveyance is operated for returning car riders tothe summit of the hump.
Track, Running. A track reserved for movementthrough a yard.
Track, Side. A track auxiliary to the main trackfor use other than as a siding.
Track, Special. All rails, track structures, andfittings other than plain unguarded track that isneither curved nor fabricated before laying.
Track, Spur. A stub track diverging from anothertrack.
Track, Stub. Track connected with another trackonly at one end.
Track, Team. Track on which cars are placedfor transfer of freight between cars and highwayvehicles.
Track, Transfer. A track so located with respectto other tracks and transferring facilities as to facil-itate transfer of lading from one car to another.
Track, Wye. Triangular arrangement of tracks onwhich cars, locomotives, and trains may be turned.
Track Bolt.A buttonhead bolt with oval neck andthreaded nut for fastening rails and joint bars.
Tread. Top surface of a railhead that contacts thewheels.
Turnout. Arrangement of a switch and frog fordiverting rolling stock from one track to another(Fig. 19.15).
Turnout Number. Number corresponding to thefrog number of the frog used in the turnout.
Turntable. A structure at the center of radialtracks that allows locomotives or cars to be turnedand positioned for movement onto any of thetracks.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Yard. System of tracks for such purposes asmaking up trains, storing cars, and sorting cars andover which movements not authorized by time-table or train order may bemade, subject to prescri-bed signals and rules or special instructions.
Yard, Flat. A yard in which car movements areaccomplished by locomotive, without material aidfrom gravity.
Yard, Gravity. Yard in which car classification isaccomplished by locomotive, with material aidfrom gravity.
Yard, Hump. Yard in which car classification isaccomplished by pushing the cars over a summit,beyond which they run by gravity.
Yard, Retarder. Hump yard equipped with retar-ders to control car speed during descent to classi-fication tracks.
Yard, Sorting. Yard in which cars are classified ingreater detail after they have passed through aclassification yard.
American Railway Engineering and Mainten-ance of Way Association (AREMA)—8201 Corpor-ate Drive, Suite 1125, Landover, Maryland 20785-2230 (301.459.3200) (www.arema.org).
19.2 Rail-TransportationSystems
There are three principal types of rail-transportationsystems: intercity passenger and freight, commuter,and rapid transit. Outstanding attributes of eachare safety, low energy requirements (a rollingresistance of 3 to 8 lb/ton for steel wheels on steelrails), ability to handle 1000 passengers or 10,000tons of freight (or more) with one train, a minimumamount of land required for right-of-way, depend-ability of service under all weather conditions, andlittle atmospheric pollution. Other types of rail-transportation systems are personal rapid transit,which has the objective of taking passengers fromone station on the line to any other station on the linewith a minimum of waiting time for a car and nointervening stops, and monorail and magnetic-levitation fixed-guideway systems.
19.2.1 Freight Systems
Generally, freight railroads are private industriesthat own or lease their right-of-way, build and
maintain their own track, structures, signal systemsand communication systems and operate trainsof owned or leased equipment. These railroadsprovide for the movement of freight between citiesacross the country and between bordering coun-tries. Freight railroads move all types of goods.Some, such as bulk goods like coal and grain, aremoved in unit trains, which are trains composedentirely of one type of car. Other goods are movedin mixed trains, which are comprised of manytypes of cars. Successful freight service dependson fair rates, consistent transit times and on-timedelivery, freedom of lading damage, and ease ofloading and unloading cargo. Good engineeringand operation are required to provide profitablefreight service.
19.2.2 Intercity and High SpeedPassenger Systems
Standard intercity passenger service provides safeand reliable movement of people across the coun-try at speeds up to 80 miles per hour. Typically,standard intercity passenger service uses tracks offreight rail companies and therefore shares thetrack with freight trains. Characteristic engineeringrequirements for a satisfactory passenger serviceinclude cars having trucks equipped with verylong travel springs, snubbers, cross stabilizers,air conditioning, good lighting, attractive decor,comfortable and roomy seats, clean and adequatetoilet facilities, convenient baggage storage, gooddining car service reasonably priced, and vista-dome lounge cars (except for overnight service).Departure times, speed, on-time arrivals, and lowfares are also important factors.
Currently, in the United States, most intercitypassenger travel is by private automobile or air-plane with only a small percentage travelling byrail. Until 1971, intercity rail passenger service wasprovided by freight railroads. Due to huge deficitsincurred for this service, Congress established aquasi-public corporation—the National RailroadPassenger Corporation, usually called Amtrak—tooperate a basic national passenger system. Rail-roads operating intercity passenger service weregiven the option to continue their own service orjoin Amtrak by contract. Railroads joining Amtrak,by payment of considerable fees, were relieved ofall responsibility for provision of intercity railpassenger service. Amtrak began operations on
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
May 1, 1971 and operated about 60% of the intercitypassenger trains that had existed before itscreation. Eventually all railroads signed contractswith Amtrak. Amtrak continues to provide inter-city rail passenger service on more than 22,000route miles in 45 states and is subsidized by thefederal government. Some state governments alsosubsidize Amtrak for specific trains that operatewithin their states.
High Speed Rail (HSR) service is generallyaccepted to be for speeds of 110 miles per hour andabove. HSR typically has its own designated trackand right-of-way separate from any freight service.Japan, Germany and France have had this servicefor many years and continue to build new routes.Recently, a French TGV traveled from Calais toMarseilles averaging 306 km/hr (190 mph). TheUnited States is just starting to develop plans forHSR in corridors where such service will providecompetitive timing to the airlines. Amtrak has star-ted HSR service in the Northeast Corridor, servingmajor cities between Washington D.C. and Boston.High Speed Rail service uses trainsets composed oftwo power cars, one on each end, with baggage cars,multiple passenger cars and a food service car be-tween the power cars. These trainsets are aerody-namically shaped to reduce airflow resistance.
19.2.3 Commuter Systems
These usually provide short-haul passenger ser-vice between a large city and its suburbs andoperate as part of a larger rail system. Peak periodsfor transportation of workers occur during earlymorning and late afternoon. But some service mustbe provided throughout the day. Important re-quirements are reliability, minimum travel time,convenience, comfort, and economy. Trains typi-cally travel on standard railroad track. They mayincorporate self-powered cars or be moved bydiesel-electric locomotives.
Automobile travel competes with commuterservice, so it is important that engineers design acommuter system that will attract the maximumpossible volume of travel. Attractions are trainsat frequent intervals, protection from inclementweather, possible saving in travel time, potentialimprovement in air quality, and economy. Somestudies indicate that rail transit in lieu of highwaysoffers lower construction costs by decreasingrequirements for right-of-way and travel lanes forautomobiles. Use of double-deck, stainless-steel
commuter cars, with air conditioning, good light-ing, and comfortable seats; on-time performanceand frequent scheduling; and push-pull operationhave resulted in substantial increase in commutertravel, even with some increase in fares.
However, even with good commuter service,railroads have been unable to operate this serviceprofitably. As a result, some states subsidize com-muter operation where it is considered advan-tageous to do so. Some large urban areas havecreated transit districts that fund developmentand operation of commuter rail systems. In severallocalities existing underutilized or abandoned rail-road freight lines have been purchased or refur-bished to establish commuter service. The justifica-tion for such state and Federal aid has been savingof money and land that would otherwise be usedfor additional expressways, relief of automobilecongestion in cities, reduction in the amount ofparking space required in cities, fewer automobileaccidents, and less noise and air pollution.
19.2.4 Rail Transit Systems
These are primarily intracity, although some pro-vide service to nearby suburbs. Characteristic re-quirements are frequent and dependable service,quick loading and unloading, light weight forrapid acceleration and deceleration, low fares, anda degree of comfort consistent with the otherrequirements.
Rapid-transit vehicles are primarily propelledby some form of external electricity. During rushhours, passengers usually have to stand for aportion of the run. In congested areas, trackagetraditionally has been located in subways or onelevated structures. In some congested areas,automobile-traffic lanes of a highway have beenreplaced by trackage. Also, in several central cityareas and major transit hub areas, transit develop-ment has led to construction of pedestrian malls inconjunction with shopping areas.
With population growth, it becomes desirable toextend or add to the rapid-transit system in somecities, and in other cities that have no rapid-transitsystem, to study the desirability of providing arapid-transit rail system or some other type ofsystem to provide adequate transportation for theincreased population. The advantages of rail rapidtransit are much the same as those given forcommuter lines. Although the likelihood of a railrapid-transit system being self-supporting is not
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
good, few cities are able to provide, on existingstreets and highways, bus service that is self-supporting.
One principal difference between commutersystems and rapid transit is that rapid transit in-volves new construction in most cases. Therefore,studies should be made to determine location andstation spacing that will be most compatible withfeeder buses at stations and will also be mostconvenient for the maximum number of people.
Rapid transit is subsidized with Federal fundsdistributed by the Federal Transit Administration(FTA), Department of Transportation (DOT), andlocal or area transit authorities. The IntermodalSurface Transportation Efficiency Act (ISTEA)sponsors utilization of all modes of transportation,including rail transit. The FTA also sponsorsresearch aimed at improvement of rapid-transitcomponents and development of new transitconcepts. European technology, especially thatapplicable to passenger vehicles, is used exten-sively for new at-grade systems.
19.2.5 Personal Rapid Transit (PRT)
Providing passengers with individualized service,PRT systems are also called Automated GuidewayTransit (AGT) or People Movers. The PRT cars arerelatively small. They are electrically operated. Thebest type of system allows a passenger to call a PRTcar to a station by pushing a button or dialing. Afterboarding, the passenger can designate the station towhich he or shewants to travel by pushing a buttonor dialing, and the car will proceed to that stationwithout stopping at any intervening station. Theobjective is to minimize waiting and transit time.The operation is completely automatic. Interfer-ence with other cars operating on the same line isprevented by computer scheduling. Ticket sellingand collecting are also automatic, using computer-controlled vending machines and turnstiles.
In the United States, new construction of freightsystems consists mostly of line changes, graderevisions, and trackage to serve new industries,mines, quarries, and provide capacity for increased
traffic. The justification for line changes isprimarily reduction of curvature to permit higherspeeds or shortening the line to reduce runningtime, to compete better for freight business. Reduc-tion of curvature and shortening of the line alsoreduce maintenance costs, helping railroads to bemore competitive with other transportation modes.The justification for grade reductions is to permitlonger trains to be hauled with one crew or toeliminate the cost of helper engines. The benefitsobtained by these measures may be determinedfrom data given in Art. 19.19. The cost of the linechanges or grade revisions should be estimatedfrom the cost of right-of-way required and the costof building the new line.
Benefits of the line or grade change should beestimated from reduced trip time, reduction inlocomotives in inventory, decrease in rolling-equipment wear, fuel savings, reduction in trackmaintenance costs, decrease in track-componentreplacement costs, and elimination of fixed-plantfacilities, including but not limited to sidings,stations, signal equipment, and road crossings. Thebenefits of new line construction for industries,mines, and quarries should be based on the addedrevenue the new lines may be expected to produceand balanced against the cost of construction,maintenance, and taxes for the added trackage.
Almost all new construction for intercity railpassenger service is contemplated to be for HighSpeed Rail. The cost benefit analysis is complex asdedicated right-of-way with no grade crossings isrequired. The location of terminals, length of theroute and speed of operation determine total traveltime from origin to destination. This, along withquality of on board service, must be comparable orbetter than equivalent airline travel.
For contemplated rail-transit, commuter, or per-sonal rapid-transit systems, the cost-benefit anal-ysis is more involved. There are also a number ofnonquantifiable benefits that should influence thefinal decision. Cost and benefit comparisonsshould be made between alternative rail-transitsystems as well as with other forms of mass tran-sit and highway systems required to move anequivalent volume of persons efficiently and cost-effectively.
Quantifiable benefits are those that produce anet economic gain and are directly attributable tothe rapid-transit system. These include land costsavings, increase in land values, savings in ridertime, reduced auto operating and parking costs,
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
less congestion for auto traffic, improvements in airquality, reduced adverse effects on the environ-ment, decreased noise pollution, less pedestriancongestion in business districts, reduced need for asecond or third car for some families, and costsavings for insurance and transportation.
The cost-benefit analysis should be made for areasonable period of time into the future and in-clude projected population growth, amortization ofequipment at the interest rate that must be paidover a period of 25 to 30 years (some equipment hasbeen used longer but should have been replacedbecause of obsolescence), and interest on the costof rapid-transit fixed facilities (roadway, stations,and shops). It is assumed that maintenance andoperating costs are included in the quantifiabletransportation cost savings.
Nonquantifiable benefits include increasedregional growth; development of community cen-ters; attraction of new industrial development;added employment in the construction, mainten-ance, and operation of the system; adequatetransportation for the young and aged; increasedaccessibility to educational, institutional, and rec-reational facilities; reduction in air pollution; andreduction in the total energy required.
Most transportation planning agencies use a15-year horizon for project planning and transpor-tation system modeling. Various scenarios aredeveloped for analyses of alternative systems todetermine the most cost-effective program fortransportation improvement for a given locality.Rail-transportation alternatives, especially whenthe Intermodal Surface Transportation EfficiencyAct is taken into account, are being selected inthose localities where population growth anddensity justify the cost.
19.4 Route Selection
As stated in Art. 19.3, new construction for freightsystems usually involves line changes, grade re-visions, or trackage to new industries. The onlyconsideration in route selection is to obtain thedesired objective at lowest cost with minimumenvironmental damage. Since grading and bridgestructureswill probably be the only items that can bevaried, use should be made of existing governmenttopographical andgeologicalmaps to the extent theywill suffice. If a considerable amount of trackage isinvolved, it will probably be desirable to have aerial
contour maps made (photogrammetry), first on alarge scale to lay out one ormore possible routes andthen at small scale along each route to arrive atestimated grading quantities.
Maximum grade and rate of curvature must beestablished before a location can be chosen. Gradeis expressed as the ratio of rise to distance in percent(a 1% grade rises 1 ft/100 ft). Rate of curvature isthe central angle, degrees, subtended by a 100-ftchord. It is desirable that both grade and rate ofcurvature be kept to aminimum, but almost alwaysa lower grade and rate of curvature mean increasedconstruction cost and sometimes a longer time.Studies should be made of several routes havingdifferent grades and rates of curvature, taking intoaccount the annual carrying charges on construc-tion cost and the estimated costs for the anticipatedtrain operation. From these studies, the grade andcurvature may be selected to give minimum costs.A calculation of running time should be made andconsidered in making this decision.
Track gage must be decided on early. Standardgage for railway track in the United States (andmany other countries) is 4 ft 81⁄2 in, measuredbetween the inner sides of the heads of the two railsof the track at a distance 5⁄8 in below the top of therails. This gage should be used if equipment is to beinterchanged with other railroads having standardgage. Locomotives, cars, and mechanized workequipment are commonly manufactured for thisgage.
A roadway cross section must also be adopted.A minimum width of roadway crown of 24 ft isrecommended for top of subgrade with subballast,ballast, and track placed on top. For sidings ormultiple track, a minimum distance between trackcenters of 15 ft is recommended. On fills, the sideslopes should be at least 1 on 11⁄2 in earth, 1 on 1⁄2 inloose rock, and 1 on 1⁄4 in solid rock (Fig. 19.1).
When aerial surveying techniques are used inconjunction with physically located control pointsalong the chosen route, preliminary and final de-sign can be accomplished with minimal field sur-veying. With computer programs developed forroadway design, engineers can prepare plans anddetermine earthwork quantities. Tying the controlpoints to the local coordinate system also allowsdevelopment of right-of-way information. Heavilywooded and bushy areas along the route, however,may cause some errors in ground elevations as wellas hide some salient features critical to projectsuccess. Hence, a personal reconnaissance of the
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
site is advisable before a final alignment has beenselected. Before construction starts, a final surveyshould be made to locate physically the controlpoints and alignment and to stake the project, toprovide adequate information for the constructioncontractor.
19.4.1 Intercity Systems
High Speed Rail systems being planned willrequire new dedicated right-of-way or substantialupgrading of existing rail routes. For new HSRsystems, there are many considerations in routeselection. These include a gentle alignment andprofile, electric power sources, environmentaleffects of construction and avoidance of any atgrade crossings.
19.4.2 Commuter and Rail-TransitSystems
Route selection for these shorter lines is deter-mined by a number of factors. Since these systemsare to serve people, a route that will be closest tothe largest number of people connecting activityhubs is to be preferred. This may be done by takinginto account the following:
Service to existing land use, which includes majoremployment areas; residential areas; institutions(hospitals, schools, churches, recreation, and otherpublic facilities); and sports, zoo, parks, and othercultural and recreational areas.
Availability of right-of-way, an important factor inthe cost. Alternative alignments that make use ofexisting right-of-way, vacant undeveloped land,and publicly owned land and streets will minimizeacquisition costs and relocation of homes andbusinesses.
Current plans and proposals for public and privateprojects that are contemplated for the future.
Impacts of proposed transit on the environment,noise, neighborhoods passed through, safety, andopportunities to enhance neighborhood growth.
For rail-transit lines, it is possible to use steepergrades than for intercity passenger and freightlines, although here again minimum practicalgrades will afford operating economies. For hori-zontal curves, the degree of curvature should bekept to the minimum practicable. The maximumcurvature permitted will depend on the desiredrunning speed, the amount of superelevationprovided, and characteristics of the rolling equip-ment. Consideration should also be given to thelength of car to be operated in a subway becausethe sharper the curve, the greater the widthrequired (due to overhang) and the higher the costof the tunnel construction.
For one rail-transit system, the following trackstandards have been established:
Tangent: desired minimum length, 500 ft andabsolute minimum, 75 ft; extension at stations,100 ft beyond length of platform.
Fig. 19.1 Typical roadbed and ballast cross section for straight single track; top ballast, about 3700 yd3/mi; subballast, about 4900 yd3/mi (includes 15% shrinkage).
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Curvature: desirable minimum radius for main-line track, 1000 ft; for yard tracks, 250 ft; minimumtrack radius for track in circular tunnels, 1000 ft.
Spiral or transition curves should be used betweentangent and curvature of 18 or more, except in yardor slow-speed trackage; also should be usedbetween compound curves.
Grades: maximum between stations, 3.5%; throughstations and at terminal storage tracks, 0.3%; otherstorage tracks and yard areas, level; minimumlength of constant-profile grade, 500 ft.
Vertical curves should be used between changes ingrade; minimum curve length, 100 times the alge-braic difference of the grades being connected, butnot less than 200 ft. Where vertical and horizontalcurves are combined and an unbalanced super-elevation in excess of 1 in is present, the lengthshould be doubled.
Reversed curves should not be used withoutincorporating the minimum tangent length orlength required for the two runoffs of elevation,whichever is greater.
Superelevation should be the equilibrium for thespeed permitted, with a maximum of 4 in. Anunbalanced elevation of up to 112 in is permitted forspeeds requiring more than 4-in elevation.
19.4.3 Right-of-Way
For intercity passenger and freight lines, the right-of-way should accommodate the number of tracksand the slope for the cuts, fills, and borrow pits.Unless a line is being located in a densely populatedarea or land cost is very high, a minimum right-of-way width of 50 ft each side of the track should beobtained. Allowance should also be made for anystations or yard facilities that may be required.
Location of receiving, classification, and depar-ture yards is governed primarily by operatingrequirements. At one time, yards were providedbetween divisions having different ruling grades.With diesel power and the need to avoid delay dueto switching, it is generally preferable to handle thesame train from origin to destination, adding ortaking off diesel units at intermediate points ifconditions justify.
Rail-transit systems in subways, at grade, or onelevated structures are advantageous in denselypopulated areas. Construction costs, effects of
construction on businesses and travel, as well aslong-term maintenance costs and effects of thetransit system on businesses and travel should beconsidered in determination of the best right-of-way for the system chosen for mass transit servinga specific area.
19.5 Track Location
Location of the tracks on prepared roadbed—including cut, fill, and sidehill cut and fill—ornatural ground surface is the most economical andis to be preferred where practicable. However, insome instances, other locations are more desirablefor reasons more important than the first cost. Thisapplies particularly to rail-transit systems that areto be constructed.
In some instances, a city has provided spacefor trackage in the median strip of expresswayswhen they were constructed, anticipating the con-struction of rapid-transit trackage at a later datewhen population growth would require it. In thiscase, the track location has already been decided.Otherwise, trackage for new rapid-transit systemsshould be constructed in open roadbed whereverpracticable.
In residential areas, the trackage should beelevated or placed in open cuts to avoid streetgrade crossings. The choice between the two islargely a matter of which costs the least from anoverall standpoint of first cost and maintenance.Open cuts will probably require reinforced con-crete retaining walls on each side of the trackage,with a chain link fence and barbed-wire outriggerson top of each retaining wall to prevent children orothers from falling into the cut. This could beavoided by use of a tunnel, but a tunnel is morecostly to construct and maintain.
Elevated trackage is in most cases preferableto cuts. It has its disadvantages, principally interms of aesthetics, and the effects of noise onnearby residents. However, in modern elevated-track construction, the track support is of eitherreinforced concrete or prestressed concrete, or acombination of the two, and of pleasing appear-ance. The elevated construction may have a ballastdeck so that the trackage can be supported onballast, which does much to reduce the noise, or therails may be supported directly on the concretefloor, in which case special fastenings will be usedwith resilient pads between the rail and the deck toreduce the noise level. Figure 19.2, for example,
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
shows the rail fasteners used in tangent trackconstruction in subways of the Toronto TransitCommission. A rubber pad is inserted under thesteel rail plate for noise and vibration attenuation.Figure 19.3 shows the Landis direct-fixation rail
fastener, developed for use on the San FranciscoBay Area Rapid Transit system and later used forother installations. This device for directly affixingrail to a rigid support structure incorporates a shearpad consisting of a 1⁄2-in-thick steel rail fasteningplate and a 1⁄4-in-thick steel base plate bonded onopposite sides of a 3⁄4-in-thick elastomeric pad. Thebase plate is bolted directly to the supportingstructure. The elastomeric pad not only insulatesthe rail plate from the base plate but permits anelastic deflection of about 1⁄4 in for attenuating noiseand vibration.
A noise level of 70 to 75 dB(A) is comparable tonoise frequently encountered in residential areas,and 70 to 80 dB(A) to usual noise in commercialand retail districts. In residential areas, tracksshould not be closer to homes than 100 to 120 ftfor elevated structures or ballast on grade or onfill. For speeds of 50 mi/h or above, a sound bar-rier should be placed between the track and anyhouse within 120 ft. In commercial and retailareas, trackage can be as close to buildings as30 ft if a sound barrier is provided. The soundbarrier may be a vertical wall extending from theground to 10 in above the bottom of the car side
Fig. 19.2 Tangent track construction used in subways of the Toronto Transit Commission.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
skirt with 8 to 10 in clearance, lined on the insidewith acoustic material. (Most of the noise fromthe rapid-transit car comes from the trucks andwheel impacts.) Such a sound barrier will lowerthe noise level about 12 dB(A). Use of continuouswelded rail with the running surface periodicallyground smooth with a grinding car or a train ofsuch cars is also helpful for reducing the noiselevel. It is also desirable to keep the car wheelsground smooth to reduce impact noise.
Placing a rapid-transit line in a subway in a mainbusiness district can eliminate the adverse effects oftrain noise and reduce street space requirements.Elevating the tracks also decreases the impact onstreet space but has the disadvantage of reducingthe penetration of daylight to the street level. Con-struction and other costs of a subway or elevatedline, however, are greater than those of a rapid-transit line at grade. Several rapid-transit systemsare in successful operation with at-grade align-ments with resilient rail supports and continuouswelded rail. Designers of these systems took intoaccount the effect on traffic. Use of resilient railsupports (Figs. 19.2 and 19.3), continuous weldedrail periodically ground, and wheels kept groundsmooth will minimize transmission of train vib-rations through the ground to nearby buildings.
19.5.1 Intercity System Capacity
For intercity passenger and freight lines, the lo-cation of passing tracks and yard tracks should betaken into account in establishing the grade line. Ifthe line is for a single track, the time it takes fortrain A to go from one passing track to the next andmeet train B and then for train B to get to the firstpassing track determines the capacity of the rail-way in trains per day. Thus, passing tracks spacedclose together afford larger line capacity than thosespaced far apart.
The sidings should be long enough for themaximum length of train to be clear of the mainline. If centralized traffic control is used, evenlonger passing tracks are desirable to permitpassing without stopping the trains.
19.5.2 Commuter and Rail-TransitSystems Capacity
Commuter and rail-transit lines will be double-track in most cases. It is necessary to have cross-
overs suitably located to permit use of only onetrack at slack periods so that track repairs can bemade, a disabled car or train bypassed, third rail ortrolley repairs made, or for other reasons. However,the addition of crossovers cannot be expected toadd much to traffic capacity of such a double-trackline. Addition of a third and fourth track would bethe most effective way to increase capacity, if thatwere needed.
In some areas with high demand at rush hour(morning and evening), commuter systems areoperating successfully over existing freight rail-road lines. These systems provide transit in themorning and evening, and freight traffic utilizesthe lines when the commuter trains are notoperating. One such system provides emergencytaxi service during the day for patrons to travelback to the suburbs.
The capacity of a double-track system is nor-mally about 40,000 passengers per track per hour.This is based on 10-car trains, with 300 passengersper car, operating at 5-min intervals. The determin-ing factor is the time required for a train to comeinto a station, unload and load passengers, anddepart from the station.
If capacities of this amount or more are con-templated, station design should be plannedaccordingly. Capacities in excess of 40,000 pertrack per hour are possible if the stations can bedesigned to handle passengers at the proposedrate. Normally, all the passengers for one trainwould not unload or load at a single station. Theexceptions are stations that serve a baseball field,football stadium, or similar facility from whichlarge numbers of passengers may be discharged ina short time, and some emergency that requiresmany passengers to leave a station swiftly.
19.6 Horizontal Curves forRailways
These include simple, compound, and reversecurves; superelevation required for such curves;and spiral curves as a means of introducing thesuperelevation on a gradual and uniform basis.
19.6.1 Simple Curves
A simple curve has a constant radius throughout.The degree of curvature generally is measured by
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
the central angle subtended by a 100-ft-long chord.Radius R, ft, and degree of curve D are related by
R ¼ 50
sin(D=2)(19:1)
For curves up to 78, length measured along thecurve is practically the same as that measured with100-ft chords. Hence, the radius R of a curve isgiven approximately by
R ¼ 36,000
2pD¼ 5730
DD , 7 (19:2)
For curves of more than 78, the error in radiusincreases with the degree of curve.
In the location or staking of the center line of asimple curve, the tangents (to its ends) should beextended, if possible, to an intersection P.I. andthe intersection angle D measured (Fig. 19.4). Thetangent distance T from the point of curve, T.C., toP.I. and from the end of curve, C.T., to P.I. may bedetermined from
T ¼ R tanD
2(19:3)
Length of curve, ft, from T.C. to C.T. is givenapproximately by
L ¼ 100D
D(19:4)
where D and D are in degrees.Stakes should be driven and tacked to mark the
T.C. and C.T. This can be done by setting a transitat P.I. and sighting along each tangent. The transitthen should be moved to the T.C., sighted on P.I.,
and D/2 turned for a check on C.T. Next, stakesshould be set every 50 ft for flat curves. Themeasurement should be made with 100-ft chordsfor curves over 78. It is good practice to markstations (100-ft intervals) around the curve and toset a stake at each station and at plus 50.
The transit deflections degrees (angle betweentangent and line from T.C. to point on the curve),for each stake equals
a ¼ LD
200(19:5)
where L ¼ length of curve, ft
D ¼ degree of curve (for a in minutes,multiply by 60)
Suppose, for example, a stake is to be set andtacked at 1108 þ 50 when the T.C. comes at1108 þ 10.5 and the degree of curve is 28 300. Alength of 50–10.5 ¼ 39.5 ft should be taped fromthe T.C. and a deflection angle of 39.5 � 2.5 � 60/200 ¼ 30 min turned with the transit, to set thestake at 1108 þ 50. For each succeeding stake, at50-ft intervals, the increment of deflection is50 � 2.5 � 60/200 ¼ 37.5 min.
19.6.2 Compound and ReverseCurves
A compound curve comprises two or more simplecurves, each successive curve having a commontangent with the preceding curve (Fig. 19.5). Thepoint of curve T.C. and end of curve C.T. are stakedas for a simple curve, although calculation of thetangent distances is more involved. The transitshould be moved to the beginning point of eachsimple curve to stake it. The degree and centralangle for each simple curve of the compound curvehave to be known or decided on in advance.Compound curves should be avoided, but theymay be used where excessive excavation or fixedobjects that must be cleared justify or require such acurve. (See also Spirals.)
A reverse curve (Fig. 19.6) is a combination oftwo simple curves with centers on opposite sidesof a common tangent. Reverse curves are accept-able in slow-speed passing and yard tracks butshould never be used in main line. A shorttangent, at least 100 ft long, but preferably more,should be placed between curves of oppositedirection in main line.Fig. 19.4 Simple curve.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
19.6.3 Superelevation of Curves
Elevation of the outer rail of a curve relative to theinner rail is desirable on main-line track. Theamount of superelevation depends on degree of
curvature and desired operating speed around thecurve. However, the amount of superelevation isusually limited to 7 in to prevent undue tilting ofthe train if it stops on the curve. For sharp curves, itmay be necessary to restrict train speed so that itwill not exceed by too much the speed for whichthe curve is elevated.
The amount of superelevation to be providedon a curve, up to the 7-in maximum, is a matterof judgment, subject to change from serviceexperience. Most freight railroads have their owncriteria, which combine speed, curvature, amountof overbalance, and length of spiral to determineallowable superelevation. Passenger-train serviceon freight lines, however, affects superelevationrequirements. Usually, and on single-track linesparticularly, not all trains will go around a givencurve at the same speed. If too little elevation isprovided for the predominating traffic and speed,the outer rail will show excessive wear on thegage side from the wheel flanges. If too muchelevation is provided, the inner rail will showexcessive flow on the top of the railhead toward
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
the gage and field sides and sometimes surfacecorrugation.
Equilibrium speed is the speed at which out-ward centrifugal force from curvature is just bal-anced by the inward component of car weightresulting from elevation of the curve. For a givendegree of curve and elevation
V ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
E
0:000149gD
s(19:6)
where V ¼ equilibrium speed, mi/h
E ¼ superelevation of outer rail, in
D ¼ degree of curve
g ¼ gage of track, ft
Permissible speed somewhat in excess ofequilibrium speed will not cause discomfort topassengers or other undesirable effects. This per-missible speed may be obtained readily from Eq.(19.6) by adding 3 in to the actual elevation ofcurve. For example, for a 38 curve with 5-insuperelevation and a track gage of 4.708 ft, theequilibrium speed is 49 mi/h. The permissiblespeed, however, is 62 mi/h (equilibrium speed for8-in elevation). Thus, the permissible speed willhave a deficiency in elevation of 3 in. This isacceptable for the type of equipment in general usein the United States. These requirements maychange as high-speed passenger trains and “tilttrains” come into use. For passenger cars havingantiroll devices, a somewhat higher deficiency ispermissible (Proceedings, American Railway Engin-eering Association, vol. 56, p. 125). For some types offreight cars having a very high center of gravity(over 96 in above top of rail), a somewhat smallerdeficiency may be desirable to guard againstderailment.
19.6.4 Spirals
An easement curve or spiral should be placedbetween tangents and each end of a simple curveand between the simple curves of a compoundcurve. A spiral increases in curvature gradually,thus avoiding an abrupt change in the rate of lateraldisplacement of cars. It also provides a means ofgradually elevating the high rail in proper relationto the degree of curvature.
Several forms of spiral may be used. The onegenerally used in the United States increases
degree of curvature with length.
d ¼ ks (19:7)
where d ¼ degree of curvature at any point
k ¼ increase in degree of curvature per100-ft station
s ¼ length in 100-ft stations from beginningof spiral to any point
The central angle d, degrees, from the beginning ofspiral, T.S. (Fig. 19.7), and the deflection a, degrees,from the tangent at T.S. vary as the square of thelength.
d ¼ 1
2ks2 (19:8)
a ¼ 1
6ks2 (19:9)
Also, the offset of the spiral, ft from either thetangent or the circular curve varies as the cube ofthe distance. Other key elements shown in Fig.19.7 may be computed from
Xo ¼ S(50� 0:000508D2) (19:10)
Ts ¼ Xo þ (RþO) tanI
2(19:11)
Es ¼ Oþ (RþO) secI
2� 1
� �(19:12)
O ¼ 0:1454DS (19:13)
where S ¼ total length of spiral in 100-ft stations
D ¼ total central angle of spiral, degrees
R ¼ radius of circular curve, ft
O ¼ offset, ft, from tangent to circular curveextended at midlength of spiral
The deflection from the tangent to the end of thespiral, S.C., with the transit set at T.S., is one-thirdof D. When the transit is set at S.C. and a backsightis taken on T.S., a deflection of 2⁄3D must be turnedoff to put the line of sight tangent to the circularcurve. The deflections for the circular curve thenshould be turned from this tangent.
Stakes on the spiral should be set every 50 ftas for a simple curve. Deflections may be calculatedto place the stakes on even stations and plus 50.Or if preferred to simplify calculation of deflec-tions, the spiral may be divided into segments ofequal length, say 10. Then, the deflection may becomputed for the first segment, multiplied by 4
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
(square of 2) to obtain the second deflection, by9 (square of 3) for the third, by 16 for the fourth(square of 4), and so on.
To set the stakes for the spiral at a distance swiththe transit at S.C., subtract the deflection computedfrom Eq. (19.9) from the deflection computed forthe same length of the circular curve extended. Thisdeflection is then turned from the tangent at S.C. tolocate each stake.
The length of spiral should be such as to givepassengers a time interval to adjust to the unbal-anced centrifugal force without feeling a jerk onentering or leaving the curve. Also, the rate ofchange of elevation should be sufficiently gradualto prevent undue twisting of the car body. Thedesired minimum length of spiral, ft, is the greaterof the lengths determined from
L ¼ 1:63EuV (19:14a)
L ¼ 62Ea (19:14b)
where V ¼ maximum train speed on curve, mi/h
Eu ¼ unbalanced elevation (deficiency), in
Ea ¼ elevation of outer rail, in
(“Manual for Railway Engineering,” AmericanRailway Engineering and Maintenance-of-WayAssociation.)
19.7 Vertical Curves forRailways
At changes in grade on main line, a vertical curveof sufficient length should be provided to preventexcessive slack action in long freight trains or asensation of discomfort to passengers at maximumspeed. Experience has shown that the rate ofchange in grade per 100-ft station on vertical curvesshould not exceed 0.10% on summits or 0.05% insags. Thus, if the grade changes from 0.20%descending to 0.20% ascending in a sag, the total
Fig. 19.7 Spiral provides transition between tangent and curved track.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
change in grade is 0.40%, and a vertical curve0.40 � 100/0.05 ¼ 800 ft long should be provided.If a similar change in grade occurs on a summit,the length of vertical curve should be 400 ft.
Ordinarily, the length of vertical curve deter-mined in this manner will not be an even numberof stations. It is simpler and satisfactory to use avertical curve of the next even number of stations;i.e., if the calculated length is 7.2 stations, use avertical curve of 8 stations.
The form of the vertical curve is parabolic in avertical plane. First, determine the elevations atthe beginning and end of the vertical curve. Addthese and divide by 2 to obtain the average.Determine the difference between this average andthe elevation at the intersection of the two grades.One-half this difference is the offset from tangent, orcorrection, to be made at the middle of the verticalcurve (Fig. 19.8). The correction at other pointsvaries as the square of the ratio of the distance fromthe nearest end of the vertical curve to half thelength of the curve. Table 19.1 illustrates themethodof calculating a vertical curve on a summit.
(C. F. Allen, “Railroad Curves and Earthwork,”and T. F. Hickerson, “Route Location and Design,”McGraw-Hill Book Company, New York (books.mcgraw-hill.com).)
19.8 Track Construction
There are several different types of track construc-tion used, depending on the type of rail-transpor-tation service and the physical characteristics of theenvironment:
Monorail One line of a suitable type of rail andrail support, with the vehicles supported above orsuspended below the monorail and electric-powered.
A monorail supported on its under side may beused for elevated construction and in subway, butif used at ground level, it must have a gradeseparation at all highway and street crossings. Asuspended monorail may be used for elevatedconstruction. Enough clearance should be pro-vided below the vehicle bottom for street andhighway crossings. Its use in tunnel and subwayconstruction would require that it be supported bythe top of the opening, resulting in a high andcostly opening. (The economics of a system intunnel or subway construction depends a greatdeal on the area of the required opening.) Also,a monorail system has disadvantages in switch-ing, weight support, construction cost, and ridequality.
Fig. 19.8 Parabolic vertical curve connects two grades at a summit.
Table 19.1 Offsets from Tangent for VerticalCurve
Length of curve ¼ þ0:35�ð�0:20Þ0:10 ¼ 5.5 stations
Use 6 stations, or 600-ft vertical curve.
Offset at P.I. ¼ 1⁄2[939.65 2 1⁄2(938.60 þ 939.05)] ¼ 0.41 ft
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Dual Rail Two lines of parallel, steel running railssupported on tie plates, ties, and ballast (Fig. 19.9)for diesel-electric- or electric-powered vehicles.
Two parallel lines of steel or concrete beams(Fig. 19.19) to provide support and guidance forelectric-powered rubber-tired vehicles.
Two parallel lines of suitably designed rails for thesupport of levitation-type vehicles, either air-cush-ion or magnetic (tracked air-cushion or Maglevvehicles), with linear-induction or turbojet motorpower for traction.
The dual rail system with ties and ballast (Fig. 19.9)which is used for the bulk of the railway track milesin the United States, and its construction are cov-ered in detail. Other systems either use some of thesame components or are proprietary, in which casethe details of construction can best be obtainedfrom the owners.
The dual-rail systems with steel wheels on steelrails, with ties and ballast, or rubber-tired wheelson steel or concrete beams (Figs. 19.16 to 19.18) can
be used for on-ground or elevated-track construc-tion. However, in subway construction, the dual-rail steel-wheel-on-steel-rail system has the railsfastened to an insulated tie plate, which is bolted tothe invert floor but separated by an insulatingand cushioning pad and insulating thimbles andwashers for the fastening bolts (Figs. 19.2 and19.3). This fastening is more economical than theprovision of additional tunnel or subway height toprovide for tie and ballast depths, even if a depth ofonly 6 in of ballast is used under the tie. The dual-rail system with rubber tires on steel or concretebeams has some disadvantage in first cost because alarger-diameter tire must be used than for the steelwheel, thus resulting in increased height of tunnelor subway opening. This, however, is to a largeextent offset by the narrower width of the openingrequired for the vehicles used in this system.
19.8.1 Roadbed
The roadbed, or subgrade, is a prepared ground onwhich to put the ballast, ties and rail. The subgrade
Fig. 19.9 Typical standard-gage, dual-rail track on tangent.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
consists of compacted soil material that supportsthe track and train loading while transmittingand distributing the load with diminishing pres-sure to the natural ground below. The importantdimensions to be considered in roadbed design arethe top width of the roadbed, the height of fill (ordepth of cut) and the side slopes of the cut orfill section. The top width of the subgrade mustaccommodate the track and ballast and may needto provide a walkway area outside of the ballastsection. The top of the roadbed may be slopeddownward away from the centerline to facilitatedrainage from the ballast. The base of the roadbedmust be wide enough to transmit the track andtrain loading within the allowable pressures of thenatural ground material. A typical roadbed sectionused on freight railroads is shown in Figure 19.9.
Subballast is a finer graded material layer,between 6 and 12 inches thick, that is placed onthe subgrade and acts as separation between thecourse rock ballast and the subgrade. The sub-ballast can also provide protection to the subgradeagainst moisture infiltration from the track struc-ture. It is most often used in mainline construction.
19.8.2 Drainage
Drainage of the roadbed and track structure is oneof the most important aspects of good railroadconstruction and maintenance. Proper drainagehelps to keep track alignment, profile and roadbedin good condition. Adequate side slopes, ditchesand openings through the roadway should beprovided. Soil that is wet or saturated has reducedbearing capacity. Undersized or blocked drainage-ways may cause flooding, washouts or settling ofembankments. Poorly drained roadbed can causeaccumulation of debris in the ballast, which leadsto tie deterioration, pumping or low joints, andproblems with track surface geometry. In coldweather, trapped moisture may lead to frostheaves, particularly at shallow culvert locations.
Intercept ditches and borrow ditches are pri-marily used to intercept surface water and carry itto nearby streams or other waterways. Typically,ditch gradients are determined by the track profile.However, a minimum gradient of 0.3% should bemaintained to avoid sedimentation buildup. Con-versely, gradients should not be so steep thaterosion occurs due to high flow velocities. Where ahigh watertable is naturally occurring, subdrainsmade out of rock, with or without perforated pipe,
may be used to intercept the water and direct itaway from the roadbed. Good drainage ofgroundwater in tunnels is an important factor inreducing track maintenance also.
Suitable drainage openings must be providedwhere the track construction crosses over water-ways. The principal factors affecting the requiredsize of a waterway opening are the area of thewatershed, slope and characteristics of the groundwithin the watershed, and maximum intensity ofrainfall that may be expected within a given periodof time. In addition, culverts or drainage structuresshould be large enough to permit easy mainten-ance and cleaning.
Many methods are available to determine themaximum flow rates, velocities and backwatercreated for particular opening sizes and configur-ations. Each railroad has their own standard asto the minimum opening required and to theallowable effects of high flows on their right-of-way and facilities. For additional information onthese methods and on waterway crossings ingeneral, see the “Manual for Railway Engineering”produced by the American Railway Engineeringand Maintenance of Way Association.
The new type of waterway opening providedmay be galvanized steel or concrete pipe; concretebox or timber, concrete, or steel bridge. Culvertpipe and box culverts should have headwalls toprevent water erosion of fill. Abutment of bridgesshould have suitable wingwalls to contain fill andprevent erosion.
19.8.3 Tunnels
Tunnels are used to pass throughmountains, underrivers or to bypass other topographic features thatcould hinder train operation. They are also used toallow trains to travel below ground in congestedurban areas. The soil conditions will determine thetype of construction necessary to keep the tunnelstable. Additional information on tunnels is foundin Section 20.
19.8.4 Fencing
Right-of-way should be fenced if it is desired tokeep off trespassers, livestock, or poultry. Postsshould be not more than 16 ft 6 in apart. Thefencing should be galvanized woven wire of No. 9gage, or galvanized steel ribbon, smooth round, orbarbed wire. The type and height of fencing are
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
dictated by the local conditions and statutoryrequirements. (For details of fencing, see AREMAManual.)
19.9 Rails and RailAccessories
Rail serves three functions. It must resist contactpressure from the wheels, it must be capable ofdistributing the wheel load over several ties alongthe track and it must be able to do this repeatedlywithout breaking. To do these, rail must be hardand have sufficient stiffness, flexural strength andfatigue strength.
To provide flexural stiffness and strength, rail isshaped in section somewhat like an I beam. Butthe head is made narrower and deeper than theflange of an ordinary I beam to resist the contactpressure and wear from flanged wheels better.Table 19.2 and Fig. 19.10 show the principaldimensions and physical properties of sectionsthat have been rolled in substantial rail tonnage or
are being rolled today in the United States. Theheavier sections are used for heavy traffic andhigh-speed lines.
The standard length of rail in the United Statesand Canada is 39 ft.
The branding rolled in raised letters on one sideof the rail web gives the weight of rail in poundsper yard, the section number, the mill, the year and
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
month rolled, and the method of manufacture. Atypical branding is as follows:
115 RE CC Manufacturer 1977 IIIII
(weight (Type) (If (Mill (Year (Month
or section controlled brand) rolled) rolled)
number) cooled)
On the opposite side of the web, the rail is hot-stamped to show the heat number, rail letter(position in the ingot), and ingot number.
Currently, only rails with weights of 115 lbs peryard or higher are manufactured unless by specialorder. Rail specifications may be found in the“Manual for Railway Engineering,” AmericanRailway Engineering and Maintenance of WayAssociation. The chemical composition of typicalrail is shown in Table 19.3. The minimum Brinellhardness specified for standard rails is 300. TheBrinell hardness in high-strength rail (alloy or heattreated) normally ranges from 340 to 380. Rail isultrasonically tested for internal defects and mustmeet specific dimensional tolerance requirementsfor sidesweep and upsweep over a 39 ft length.
Control cooling of rail (retarding the cooling rateunder controlled conditions) is effective in pre-venting shatter cracks. These may lead to develop-ment of transverse fissures in service, so controlcooling is included in rail specifications, exceptwhen rails are made from vacuum degassed steel.
On curves, many railroads use fully heat-treatedrail, which has the top part of the head heat-treated,or alloy-steel rail, to withstand better the flangewear that occurs on the high rail of curves and theflow and corrugation that occur on the low rail.
19.9.1 Stress and Strain in Rails
Rail stresses and depressions for unusually heavyloads may be computed by considering a rail as a
continuous beam on an elastic support (AmericanRailway Engineering Association Proceedings, vol. 19,pp. 878-896). With the tie spacings in general use,the assumption that rail is continuously supportedwill not cause significant error. The modulus ofelasticity of rail support u is the uniform load, lb/lin in of rail, required to depress the rail 1 in. It isfurther assumed that the pressure, lb/in, of the railon its support at any point is
p ¼ uy (19:15)
where y ¼ rail depression, in. Another significantterm is the distanceX1, in, from point of applicationof a wheel load to the point where the bendingmoment caused by that load becomes zero andthen reverses in direction.
X1 ¼ p
4
ffiffiffiffiffiffiffiffi4EI
u
4
r(19:16)
where E ¼ modulus of elasticity of rail steel(30,000 ksi)
I ¼ moment of inertia of rail, in4
For a single wheel load, the bending momentand rail depression along a rail may be determinedin terms of Mo and Yo from Fig. 19.11.
Mo ¼ 0:318PX1 (19:17)
Yo ¼ �0:393P
uX1(19:18)
where P ¼ wheel load, lb
Mo ¼ bending moment due to wheel load,in-lb
Yo ¼ rail depression under wheel load, in
Since there is always more than one wheel load,the master diagram may be used to determine themoment and depression at any point in the rail forall wheels by taking one wheel at a time andcombining the effects algebraically. The maximumflexural stress in the rail base at this point may thenbe determined by dividing the total bendingmoment by the section modulus of the rail for thebase. The tie load or reaction can be determined bycalculating the average rail depression for the tiespacing and multiplying by the tie spacing andmodulus u.
The value of u must be determined by actualmeasurement in track. This value ranges from 500
Table 19.3 Limitations on Chemical Content ofSteel Rails, Percentage by Weight
Nominal weight of rail, lb/yd 115 or more
Carbon 0.72 to 0.82Manganese 0.80 to 1.1Silicon 0.10 to 0.60Phosphorus, max. 0.035Sulfur, max. 0.037
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
for track with little ballast and poorly compactedroadbed to 2000 or more on track with adequateballast and well-compacted roadbed. The value ofu is not critical in calculating rail stresses but issignificant for rail depression.
There is no established impact effect or per-missible working stress in rail because of varia-bility of conditions on different railways. Thefollowing may be used as a guide: Multiply thestress for static loads by a percent impact factor of33V/D, where V is the speed, mi/h, and D thewheel diameter, in. Thus, with a 36-in-diameterwheel at 60 mi/h, the impact factor is 55%. Aflexural stress at the extreme fiber of the base injointed track of 35 ksi is permissible at speedsbelow 35 mi/h, or 30 ksi at higher speeds; incontinuous welded rail, 25 ksi.
Figure 19.12 shows the bending stresses calcu-lated by this method for a typical 100-ton freight
car with four-wheel trucks. An approximate valueof stress for other weights may be determined bymultiplying the values shown by the ratio of thewheel weights on the rail.
19.9.2 Continuous Welded Rail
For new rail, most railways use continuous weldedrail (CWR). It is usually placed in quarter-milelengths, which are delivered to the job site inspecial trains. When in place in the track, the railsare welded end to end by a thermite weldingprocess. In an alternative welding process, mach-ines are used to butt weld in the field in the samemanner as in the shop. Secondhand bolted rail iscropped to remove worn and battered ends andbolt holes and then is butt-welded before it is laidin track. However, any length of continuous railthat is 400 feet or longer is considered to be CWR.
Fig. 19.11 Diagram for calculating rail bending moment and depression under a single wheel load.(ASCE-AREA Special Committee on Stresses in Railroad Track.)
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Expansion and contraction of continuous wel-ded rail are controlled by the rail joints and the railfastenings or anchors. The restraint stresses the rail.A tensile stress of 195 psi is produced in the rail bya 1 8F temperature drop. For example, if continu-ous welded rail is laid at 70 8F and the railtemperature drops to 230 8F, a tensile stress of19,500 psi develops in the rail because it is res-trained from shortening.
When the rail temperature increases above thelaying temperature, compressive stresses developin the rail due to the restrained ends of the railstring. The force developed by these stresses willcause the rail to move sideways. Unless this forceis restrained, the rail and track will buckle.This movement is prevented by the use of railanchors and sufficient ballast shoulders. The railanchors provide a relatively uniform distributionof the lateral rail force to the ties and the ballastshoulder provides resistance to lateral tie move-ment. A minimum top of ballast shoulder width of12 in is recommended. When the rail temperaturedecreases below the laying temperature, the railtries to contract and induces tension at rail joints.The restraint at rail joints from track bolt shearstrength and rail-joint friction may not be enough
to maintain the joint integrity and a pull-apart willoccur. Additional rail anchors are used to restrainmovement of the rail at joint locations (see Article19.9.4).
An effort is made to lay continuous welded railat about a mean temperature, which may requirethe rail to be heated or cooled. This is not alwayspractical, so it may be desirable to adjust the raillength later if difficulty with track buckling or jointpull-aparts occurs.
19.9.3 Jointed Rail
Jointed rail is made up of short rail lengths (33 to 39feet) joined together by joint bars with track bolts.This was the standard type of track before thedevelopment of continuous welded rail but is stillwidely used. Jointed rail in mainlines requires ahigher level of maintenance than CWR. Wheelimpacts at joints can cause rail end batter, looseor broken bolts and track surface geometry deteri-oration.
Rail-joint bars are used to join together abuttingrails. As an alternative, rail is butt-welded into longlengths before it is laid in track. The welded stringsare joined with rail-joint bars or thermite welds.
Fig. 19.12 Calculated rail stresses produced by a typical 100-ton-capacity hopper car (gross loadof 263,000 lb). Recommended work stresses: (a) Jointed rail on branch line with speeds under 35 mi/h;(b) jointed rail on main line; (c) continuous welded rail on main line.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
In jointed tracks, most railways use two 36-injoint bars with six bolts and spring washers perrail joint (Fig. 19.13). There are 271 rail joints permile of jointed track.
In years past, joint bars were shaped some-what like an angle in cross section and werecalled angle bars. Since about 1930, most jointbars have been shaped more like an I beam andare called joint bars or sometimes short-toe jointbars, to distinguish them from the long-toe anglebar. Headfree bars fit into the upper fillet betweenrail web and head. Take-up for contact-surface(fishing-surface) wear is provided in the base.Head contact bars have a slope on both the headand the base to match the fishing surfaces of therail, and take-up for wear is provided at bothhead and base. Results with both types of barshave been equal in service tests. The “Manual forRailway and Maintenance of Way Engineering,”American Railway Engineering Association, givesdesigns of joint bars for 115 RE, 119 RE, 132 RE,133 RE, 136 RE, and 140 RE rail. Steel companiesthat roll joint bars can furnish design drawings ofbars they are equipped to roll.
Most rail-joint bars are made of oil-quenchedcarbon steel, manufactured in accordance withspecifications given in the AREMA Manual, orASTM Standards. Carbon is specified at 0.35 to0.60%; manganese, not over 1.20%; and phos-phorus, not over 0.04%. Tensile strength of 100 ksi,yield point of 70 ksi, 12% elongation in 2 in, and
25% reduction of area are minimum requirements.A bend test is also required. Brinell hardness is notspecified but usually varies from 225 to 275.
Rail-joint bars are punched with alternate ovaland circular holes. Hence, the bars can be used oneither side of the rail and always have an oval andcircular hole match for the track bolt. Track boltsfor 115 RE, 119 RE and 133 RE rail are 1-in diam-eter. Track bolts for 132 RE, 136 RE and 140 RE railare 1-1⁄8 in diameter. Bar punching is spaced6-6-71⁄8 -6-6 in/(AREMA Manual).
It is important that the bars be straight orcambered in the least harmful direction. For 36-inbars, a camber of 1⁄16 in in either direction in thehorizontal plane is acceptable. But in the verticalplane, the bar may not be low or more than 1⁄16 inhigh at midlength.
19.9.3 Track Bolts
These are used for bolting a pair of joint bars inposition. Most railways purchase heat-treatedcarbon-steel track bolts and carbon-steel nuts inaccordance with specifications in the AREMAManual or ASTM Standards. Track bolts have aforged button-type head with either an oval orelliptic neck to prevent turning in the joint bar. Thethreads are rolled. Most railways specify a Class 2or finger-free fit. The bolt-and-nut design is inaccordance with American National StandardsInstitute Standard B18.2. A minimum carbon of
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
0.30%, maximum phosphorus of 0.04%, and maxi-mum sulfur of 0.06% are specified. Tensile strengthof 110 ksi, yield point of 80 ksi, 12% elongationin 2 in, and 25% reduction in area are minimumrequirements. A bend test is specified, as is theminimum tension load that the bolt with nut fullyengaged must withstand without stripping the nutor breaking the bolt. For the 1-in-nominal-diameterbolt, this is 66,560 lb; 11⁄6-in, 76,360 lb; and 11⁄8 -in,83,900 lb. Initial bolt tension in track of 20,000 to30,000 lb is recommended. Larger-diameter boltshave some value in resisting bending from thecontraction force in the rail in cold weather.
Spring washers are used to maintain bolttension and reduce the amount of bolt tighteningrequired. Tests have shown that track bolts becomeloose because of fishing-surface wear, whichpermits the joint bars to move closer together, notbecause of vibration. Specifications for springwashers in the AREMA Manual require that, witha release of 0.03 in from an initial compression of20,000 lb, spring washers will maintain a reactiveforce of at least 5000 lb. This amount of release isadequate for the fishing wear that occurs in a year’sservice, regardless of traffic, and a bolt tension of5000 lb is sufficient to ensure proper functioning ofthe rail joint.
The high initial tension allows for properseating of the joint bar and some subsequentrelaxation of tension in service. Tension of in-service bolts should range from 15,000 to 25,000 lbs.Bolts must be checked for proper tension at regularintervals.
19.9.4 Rail Anchors
A rail anchor is a device used to restrain lengthwisemovement of rail. There aremany different types inuse. Most types engage the rail base by a springclamping action and bear against the side of the tieor tie plate to restrain rail movement. The anchorshould have sufficient holding power to move thetie in the ballast rather than permit the rail to slipthrough the anchor. Figure 19.14 shows a goodmethod for anchoring jointed track with this typeof anchor (AREMA Manual).
For continuous welded rail, every other tieshould be have rail anchors applied on both railson both sides of the tie. This is called box anchor-ing. Box anchoring will provide effective resistanceto longitudinal stresses in the rail from temperature
changes and train movements. Where interrup-tions in CWR occur, such as at turnouts orcrossings, every tie within 200 feet of the interrup-tion, in both directions, should be box anchored.
19.9.5 Tie Plates
A rolled-steel plate is used between rail and tie todistribute the rail load, reduce tie abrasion andhold the rail to gage better. The trend has beentoward larger tie plates and use of double shoul-ders, instead of just one shoulder to restrain theouter edge of the rail base. The plates, rolled to thedesired cross section, are sheared to a widthgenerally of 73⁄4 or 8 in. A cant of 1 :40 is providedin the rail seat to incline the rail slightly inward. Tieplates having a length of 12 to 14 in are commonlyused in the United States for rails having a basewidth of 51⁄2 in and a length of 13 to 16 in for railswith a base width of 6 in. A greater length of tieplate is provided on the field side of the rail than onthe gage side (from 1⁄2 to 21⁄2 in) to better resist theoutward lateral forces on the rail on curves.
Fig. 19.14 Methods of anchoring jointed track.(a) For main track carrying traffic essentially in onedirection. Under average conditions, with any typeof ballast, use eight forward and two backupanchors per 39-ft rail length. (b) For main trackcarrying traffic in both directions. Under averageconditions, with any type of ballast, use eightanchors per 39-ft rail length to resist movement ineach direction, a total of 16.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Generally, tie plates have four holes, 3⁄4 insquare, punched through the shoulders for spikesto hold the rail to line. The plates also have fourholes, 11⁄16 in square, punched near the corners fortie-plate fastening or hold-down spikes (Fig. 19.9).On tangent track, it is usual practice to use two linespikes in staggered holes for each tie plate.Sometimes, two hold-down spikes are used inoppositely staggered holes. On curves, two lineand two hold-down spikes are used per plate. Oncurves of 68 and over with heavy traffic density, anadditional line spike is used at the inner edge of therail base. Some tie plates that are designed for usewith elastic rail clips may have special configur-ations to allow for attachment of the clips to theplate.
Tie plates are made by various processes,generally by open-hearth or basic-oxygen. Carboncontent varies from a minimum of 0.15% forlow-carbon plates to a maximum of 0.85% for high-carbon plates. Low-carbon plates may be cold-worked; high-carbon plates must be hot-worked.Designs and specifications may be found in ASTMStandards and the AREMA Manual.
19.9.6 Rail Fastening
Rail fasteners consist of any device or system ofcomponents used to fasten the rail to the tie or othersupport. Many different types of rail fasteners arein use today. The most widely used is the steel cutspike. However, elastic or rigid steel clips and driveor screw spikes also are used. Rail fasteners pro-vide restraint against vertical, lateral and rotationalmovement of the rail. They are also used to anchortie plates to the ties. Some fasteners, such as elasticclips may provide some restraint against longitudi-nal movement of the rail as well.
Cut spikes are usually used to fasten rails to ties.They are formed with a wedge-shaped point to cutthe tie fibers and prevent splitting. The head isrounded on top to facilitate driving; it is oval inshape and eccentric on the shank to provide alength of 11⁄16 in to engage the top of the rail base.See also Art. 19.11.2.
Line spikes, for holding rails to gage, arecommonly 5⁄8 in square and 6 in long under thehead. Hold-down spikes, for fastening tie plates toties, are commonly 9⁄16 in square and 51⁄2 in longunder the head. A copper content of 0.20% issometimes specified to give corrosion resistance.
For design and specifications, see ASTM Standardsand the AREMA Manual.
Rail clips are designed to have contact with boththe top surface of the rail base and the tie or railsupport. Elastic clips are designed to deformmeasurably under load but return to their initialcondition when unloaded. Rigid clips do notdeform measurably under load. Clips may fit intospecial slots in the tie plate or be anchored to thesupport with bolts or screws.
Drive spikes, also known as screw spikes, aresteel screwswith square heads that may be used fortie plate hold downs, timber crossing hold downsand other timber applications. Drive spikes havematerial properties similar to cut spikes and comein diameters of 1⁄2to
3⁄4 in.
19.10 Ties
Cross ties provide support for the rails anddistribute rail loads to the ballast. Switch ties servethe same purpose as standard cross ties but arelonger to support the widened sections of turnoutsor railroad crossings. Ties are made of many typesof materials, including wood, concrete, steel andcomposite materials. Most ties in railway track inthe United States are of treated wood, mostly oak,gum, pine, or fir. For main-line track, the mostcommon size is 7 � 9 in by 9 ft long. Smaller sizesare used for yard tracks, such as 6 � 8 in by 8 ftlong. Ties are sawn rather than hewn and consistmostly of heartwood. This part of the tree is lessdesirable for lumber but more desirable for ties.Generally, ties containing the following will not beaccepted by purchasers: decay; a hole more than3 in deep and 1⁄2 in in diameter when between 20and 40 in from midlength, or more than one-fourththe width of the surface on which it appears whenoutside the sections of the tie between 20 and 40 infrom its middle; a knot having an average diameterin excess of one-fourth the width of the surface onwhich it appears, except when outside the same 20-to 40-in zone; a shake larger than one-third the tiewidth; a split more than 5 in long; and a slant ingrain in excess of 1 in 15 (AREMA manual).
When ties are received at the treating plant forseasoning, some railroads apply antisplittingdevices, such as nail plates, to some or all ties. Tiesshould be seasoned prior to treatment with pre-servatives. Traditionally, air seasoning has beenusedwherein ties are stacked such that air flow is main-
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
tained around the ties to dry them to the propermoisture content. As this is a natural drying process,it is time consuming. Other seasoning methodsinclude Boulton Drying, vapor drying and steamconditioning. Different types of wood responddifferently to these methods and therefore careshould be taken to select the best method.
Seasoning removes sufficient moisture from thewood to permit addition of a preservative. Beforethe seasoned ties are treated with preservatives,they should be adzed for the tie plates and boredfor the track spikes.
Ties are treated with preservatives to preventdecay and extend the life of the tie. Coal Tar Creos-ote or mixtures with coal tar or heavy petroleum arethe primary preservatives used. Treatment resultsaremeasured in pounds percubic foot of retention ofthe preservative. Depending on the wood type,retention of coal tar or petroleum-based preserva-tives should be between 6 and 8 pcf. Other pre-servatives, such as water-born salt or pentachloro-phenol, may also be used. Tie treatments must meetspecifications C-6 of the American Wood PreserversAssociation (AWPA).
Prestressed concrete ties are used in locationswith heavy tonnage, high traffic volume or wheresteep grades or sharp curves are present. Prestres-sed concrete ties are manufactured with dimen-sions similar to wood ties. Inserts for rail fastenersare cast into the concrete. Tie plates are not used butinsulating or cushioning pads are placed beneaththe rail to absorb impact and prevent signalcurrents in the rail from entering the ties. Concretestrengths are generally 7000 psi and above.
Steel ties are oftenused in locationswhere verticalclearance is a factor. Due to the design of the steelties, the distance from top of tie to bottomof ballast isless than for standard wood or concrete ties. Tiesmade of composite materials are being developedand tested to determine if they have the durabilityand flexibility to be used as replacement ties.
On most existing track, ties are renewed only asrequired or on a spot renewal basis. Prestressed-concrete ties should be placed out of face to givebest results. Therefore, they are less economical fortie renewals in existing track.
19.11 Ballast
Ballast supports the ties, restricts movement of theties and transmits rail loads to the subgrade or
roadbed. Ballast also absorbs impact loads. Typeand gradation of the material to be used for ballastand the cross section are important with respect tothe cost of maintaining line and surface. This costmust be balanced against the original cost. In newtrack construction, best results can usually beobtained by placing a layer of subballast on top ofthe roadway and supporting the track structure,including the topballast, on this layer. Thesubballast should be small particles of a materialthat will not disintegrate. Its purpose is to providedrainage and keep the subgrade from penetrat-ing up into the topballast while wet and underpressure. Stone or slag screenings, chat (residueafter extracting ore from rock), and sand makeacceptable subballast. Subballast should be placedin layers and thoroughly compacted.
The topballast may be of hard rock crushed tosuitable size; crushed blast-furnace or properlyprocessed open-hearth slag; or crushed gravel, ifthere is a sufficient quantity of angular material toprevent rolling. Individual railroads have differentpreferences for size of ballast. For complete speci-fications for ballast materials, see “Manual forRailway Engineering,” American Railway Engin-eering and Maintenance of Way Association.
A recommended ballast section is shown in Fig.19.11. A 12-in depth of top-ballast below the bottomof the ties and a 12-in depth of subballast willgenerally provide good track support for heavyloading and traffic (AREMA Manual). As theroadbed becomes further compacted by traffic, itwill be necessary to add additional ballast to re-surface the track from time to time. After severalyears of service, the depth of ballast under the tieswill probably be considerably increased. If over-head clearances are reduced due to the additionalballast depth, undercutting may be done to removeexcess ballast. Ballast may also become fouled fromballast particle degradation or other sources.Fouled ballast does not provide for drainage ofwater away from the ties and rail and should becleaned or replaced.
19.12 Turnouts and Crossings
A turnout provides the means for trains to bedirected from one track to another. A turnout ismade up of a pair of switch points with accessor-ies, a frog, a pair of guardrails, and a set of turnoutties (Fig. 19.15).
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
19.12.1 Frogs
A frog is a special unit of trackwork that permitstwo rails to cross. It is designated by number andtype.
The frog number is the ratio of the distance fromthe intersection of two gage lines to the spread, ordistance between gage lines, at that distance. Thenumber also is given by half the cotangent of halfthe frog angle. The frog number determines thefrog angle, the degree of turnout curvature, andthe lead, or distance from the point of switch to thepoint of frog. Table 19.4 gives these data for frognumbers from 5 to 20. Since speed is limited bycurvature, the frogs with sharper turnout, thesmaller-numbered ones, are used in yard trackswhere speed is slow. The larger-numbered frogsare used in main-line locations to permit desiredspeed to the extent practical. Where extremelyshallow frog angles are used, particularly inhigh speed operations, a movable point frog maybe used. The movable point eliminates the longflangeway gap at the intersection of the flangewayscaused by the shallow angle. In turnouts, themovable point control is tied to the switch controlso that the frog point is always in the correctposition for train movements through the switch.
Frogs are either rigid or spring-rail types. Rigidfrogs are of bolted rail, rail-boundmanganese-steel,or solid manganese-steel construction. In a bolted-rail rigid frog, components are made from regularrolled rail, planed or machined as required. Theassembly is held together by bolts through the railwebs, with the components separated by fillerblocks to form the flangeway. A rail-boundmanganese-steel frog (Fig. 19.16) includes a castinsert of Hadfield manganese steel, which formsthe point and wings, the locations most subject toimpact, batter, and wear. (Hadfield manganese
steel is a high-manganese alloy, which whenproperly heat-treated increases in hardness withcold working, so it is especially well-suited to resistbatter at frog corners.) The insert is supported bybent sections of rail, and the assembly is fastenedtogether with bolts through the binding rails andthe insert. A solid manganese-steel rigid frog (Fig.19.16b) is made entirely of cast Hadfield manga-nese steel. It usually is self-guarded to save the costof separate guardrails. The frog is joined to the tworunning rails at toe and heel by regular rail-jointbars and connecting bolts.
A spring-rail frog is made of machined rail sec-tions. One side of the frog has a regular flangewaylike a bolted-rail rigid frog. This is placed in themain running track. The other, or turnout, side, hasa spring wing rail, which normally is held againstthe side of the frog point. Wheels passing throughthe turnout side force the spring rail out, againstspring resistance, to provide a flangeway. Thespring-rail frog provides a continuous runningsurface with a minimum of impact for the mainrunning track.
Spring-type frogs are not recommended wherethere are many movements through the turnoutside requiring frequent opening of the spring rail oron the outside of curves. Bolted-rail frogs cost theleast, but they do not last as long and require moremaintenance than the rail-bound or solid manga-nese. Self-guarded solid manganese frogs are usedmostly for the smaller-numbered frogs in yardtracks where speeds are relatively slow.
19.12.2 Guardrails
A guardrail is fastened to each rail directlyopposite the frog point, to contact the back of eachpassing wheel and prevent the flange of its mating
Fig. 19.15 Crossover consists of two turnouts and a crossover (connecting) track. Numbers indicatedimensions given in Table 19.4
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
wheel on the axle from going down the wrong sideof the frog point. Guardrails are of rail or cast-manganese-steel construction. The ends are flaredinwardly of the track to engage the back of thewheel flanges and guide the pair of wheels on eachaxle into proper lateral position in the track. It isimportant that the guardrails be long enough andproperly positioned to ensure that the wheels areguarded past the frog point. It is also importantthat the guard check gage (distance between guardand gage lines) be maintained at not less than 4 ft65⁄8 in (for standard gage). Guardrails are notrequired with self-guarded frogs.
19.12.3 Switches
A switch consists of a pair of switch points, a set ofswitch slide plates with braces, main and connect-ing rods, and a manually or power-actuated switchstand (Fig. 19.17). The switch-point rails are planedfrom regular rolled rail and reinforced on each sideof the web with steel straps riveted in place. Heelblocks are used to join each switch-point rail to theadjoining lead rail, and both are fastened to theother running rail.
The heel spread (distance between the two gagelines) is 61⁄4 in, so the switch angle is fixed by thisdistance and the length of the switch-point rail. Ashort switch point and large angle are satisfactoryfor slow-speed operation. For example, a 16-ft 6-in
length of point is satisfactory for a No. 8 turnout.For a high-speed turnout, such as a No. 20, 30-ftpoints are used.
Usually, switch points are made straight. But forhigh speeds, the switch points are sometimescurved and 39 ft long for No. 18 and 20 turnouts.Comfortable operating speeds through turnoutsare shown in Table 19.4.
Switch ties must be provided for turnouts.These are usually spaced on about 20-in centers.Two long ties must be provided at the switch pointfor the switch stand. Each tie thereafter is madelong enough to extend from each outer rail base thesame distance as on regular track. Whenever theswitch tie becomes as long as twice the length of aregular tie, the switch ties are discontinued andregular ties used.
19.12.4 Crossings
A crossing of two tracks requires four crossingfrogs, frog plates, and crossing ties. Crossing frogsare made of bolted rails with either regular control-cooled rail or heat-treated rail; of rail-bound man-ganese-steel castings; or of all manganese-steelcastings. Each running rail has a guardrail with a2-in-wide flangeway between. To ensure that suchguardrails are effective in preventing the wheelflanges from entering the wrong side of the point,crossings should not be made with an angle of less
Fig. 19.16 Frogs used where rails intersect. (a) Rail-boundmanganese-steel frog for main line. (b) Solidmanganese-steel self-guarded frog for yard tracks.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
than 98 360 on tangents. (For curves, see AmericanRailway Engineering and Maintenance of WayAssociation Trackwork Plan No. 820.)
It is desirable to locate crossings on tangent onboth intersecting tracks, but when this is not prac-tical, crossings can be made to fit any condition ofcurvature.
19.12.5 Trackwork Plans
Details and specification of material required forturnouts and crossings are given in the TrackworkPlans of the American Railway Engineering andMaintenance of Way Association (AREMA). Somemajor freight railroads, however, have their ownstandard plans and specifications for this materialand these differ from those of the AREMA. Whentrackwork material is to be ordered for a railroad,first the standards to be used should be determinedand then the railroad and plan number should bespecified and specifications given. When crossingsare to be ordered, the intersection angle, the curva-ture, if any, and the rail size should be specified.
19.13 Culverts, Trestles, andBridges
Culverts provide waterway openings under tracks.Usually, culverts consist of galvanized corruga
ted pipe or arches, reinforced concrete pipe, orreinforced concrete rigid-frame boxes. They arecheaper to install and maintain than other types ofopenings.
Care must be exercised in placing the fill on thesides and over the larger-sized culverts becauseside pressure against the culvert is a large factor inits ability to support vertical pressure. Metalculverts of up to 180 ft2 and reinforced concreteculverts of up to 300 ft2 in opening area are in use.
Trestles often are built of treated-timberstringers supported on capped and braced trea-ted-timber piles. Trestles have either an open deckor ballasted deck. Ballasted decks are moreexpensive in first cost but require less work tokeep the track in line and surface and offer less of afire hazard Treated-timber trestles are economical,have a life of 40 years or more, and require nopainting.
Trestles are also constructed of steel or concretepiles, either reinforced or prestressed, with aconcrete cap supporting steel or concrete stringers.Concrete trestles usually have ballasted decks.Steel trestles may have open or ballasted decks.
Bridges generally are built of steel, reinforcedconcrete, or prestressed concrete. Usually, theabutments and piers are of reinforced concrete.For steel bridges, rolled beams are generally usedfor spans up to 50 ft. Plate girders of bolted orwelded construction may be used for spans up to
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
about 150 ft, and trusses, either through or decktype, for longer spans. Open or ballasted decks areplaced on steel bridges. Ballasted decks, however,are preferred for all types of bridges because of easeof track maintenance and reduction of impact.
“Manual for Railway Engineering,” AmericanRailway Engineering and Maintenance of WayAssociation, gives recommended designs and speci-fications for construction of all types of bridges,trestles, and culverts. These include recommen-dations for live load in terms of Cooper’s E loading,allowance for impact effects, and permissible designstresses. (See also Sec. 17.)
19.14 Maintenance of Way
After a railway is completed, continual mainten-ance is required to keep it in condition for opera-tion. Mechanized equipment is used for this to amajor extent in the United States.
On-track equipment, such as Jordan spreadersand shovels, and off-track equipment, such asbulldozers, shovels, draglines, and special track-mounted ditching machines may be used forditching. Side-dump cars may be used fortransporting material from ditches in cuts for bankwidening on fills. Chemical weed killers or trackburners may be used to keep the ballast sectionclear of vegetation. Chemical weed and brush kil-lers or power mowers or cutters may be used tocontrol undesirable weeds and brush on the right-of-way. Ballast-cleaning equipment is available forcleaning ballast between ties, in the ballast shoul-ders, and under the ties.
19.14.1 Track Maintenance
Maintenance of track structure includes, tie re-newals, periodic tightening of track bolts, raisingthe track to correct variations in surface and crosslevel, lining the track to correct deviations fromalignment, and adding ballast and dressing theballast section.
Use of continuous welded rail increases thelikelihood of track buckling in very hot weatherand rail pull-aparts in very cold weather. A studyof a large number of track buckles that occurredover 3 years on a major railroad indicated thefollowing:
The principal causes of track buckling areinadequate ballast, disturbing the tie bed during
tie renewals or track surfacing, and improper raillaying or adjusting for temperature. Track bucklesare more likely to occur during hot spells in thespring in the afternoon. They are also more likely tooccur on curves than on tangent track, and theprobability of occurrence increases as the degree ofcurvature increases.
Derailments caused by track buckles can beminimized by maintaining a full ballast section,using care not to disturb track in very hot weather,and inspecting track in the afternoons of the firstdays of early hot spells. In addition, appropriatemeasures should be taken by issuing slow ordersand by track strengthening or stress relieving therail when track buckles or impending track bucklesare observed. (AAR Research and Test DepartmentReport R-454, “An Investigation of RailroadMaintenance Practices to Prevent Track Buckling,”Association of American Railroads, 50 F St., NW,Washington, DC 20001.
String lining is a convenient and satisfactorymethod of checking the alignment of curves. Thismay be done manually or with automated equip-ment found on some tamper/liner work equip-ment. The manual procedure requires that theoutside rail be marked in 15.5 or 31 foot stations.Then the mid-ordinate of a 62 ft string line or chordis measured at each station. The mid-ordinate,measured in inches, indicates the degree ofcurvature at that station. Calculations can be madebased on the mid-ordinates to determine theamount of track shift necessary to obtain a uniformcurve. Automated equipment will document themeasurements and translate the calculated shiftsdirectly to the track liner. Automated equipmentwill create a uniformly smooth curve but the curvemay not be at a specific degree of curvature.
19.14.2 Rail Life
This is usually expressed in million gross tons oftraffic carried before rail must be replaced. Grosstons equal the total weight of the locomotives andcars and their loading, short tons.
Rail life is determined by a number of factors:
1. Size of the Rail. The heavier sections, such asthe 140 RE, 136 RE, and 132 RE, will have alonger rail life than the lighter sections, suchas the 100 RE, 115 RE, and 119 RE, undercomparable operating conditions.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
2. Curvature. In general, rails do not have as long alife on curves as on tangent track; the sharperthe curve, the shorter is the rail life. Adequatelubrication of the outer rail on curves willgreatly extend the rail life.
3. Wheel Load. The life of rail under 100-ton cars isappreciably less than under 70-ton cars butlonger than under 125-ton cars. The contact pres-sures from the wheel loads of the heavier carsincrease wear on the gage side of the outer railand plastic flow on the top and sides of the headon the inner rail of curves faster than the increasein wheel loads. Also, the wheel loads from theheavier cars cause a disproportionate increasein the number of rail failures (“Comparison ofRail Behavior with 125-ton and 100-ton Cars,”D. H. Stone, AREA Proceedings, vol. 81, p. 576.)
4. Continuous Welded Rail (CWR). This hasmade a decided improvement in the service lifeof rail on tangent track. With jointed rail, theprincipal factors determining rail life are fishing-surface wear and rail-end batter at rail joints.With CWR, there are no rail joints, only shop orfield butt welds, except at insulated joints. (Therelatively few insulated joints are now generallyglued to prevent rail-end movement within thejoint bars.) The rail life of CWR on tangent trackand light curves (18 or under) is determined bythe number of service and detected rail failures.These are mostly transverse, progressive frac-tures within the head, which increase in fre-quency with the cumulative number of wheelloadings. At some point, the frequency ofoccurrence of such failures makes it moreeconomical to replace the rail than to cut outthe failures or detected defects and weld in alength of repair rail.
5. Metallurgy. Most railways use alloy or heat-treated rail on very sharp curves. This decreasesthe rate of side wear on the outer rail and theplastic flow on the top and sides of the inner railand thus materially extends the rail life.
6. Need for Relay Rail. This may be a factor in raillife. Either jointed rail or CWR may be removedalthough it would have further service life ifthere is a requirement for this rail for relaypurposes on curves, branch lines, yard, orindustry tracks.
7. Corrugation. This may be a factor in rail life,although grinding trains are usually used to
correct this rail surface condition unless it getstoo bad.
8. Available Funds. Availability of funds topurchase and lay new rails is a practicalconsideration in rail life. If funds are lacking,the rail life may be prolonged beyond the mosteconomical life.
Track lubricators reduce flange wear of outerrails and curve resistance to train movement. Thedevices are fastened to the rails at curves to applylubricant to the flange of each passing wheel.Generally, a track lubricator consists of a reservoircontaining a suitable type of grease, an applicator,and a plunger activated by each passing wheel topump a small quantity of grease into the applicator.The applicator is a steel member, several feet long,placed against the gage side of the rail and in-corporating small holes through which the greaseis pumped to contact wheel flanges. Several typesof lubricators are available. Manufacturer’s inst-ructions should be followed with respect to loca-tion and type of lubricant.
Some lubricators are designed for applicationfrom hi-rail or track inspection vehicles. Thismethod allows applications to be made at anylocation, not just fixed points, when the rail is toodry. With either method, care should be taken tominimize the chance of lubricant building up onthe top of the rail where it may cause locomotivetraction may be reduced.
19.14.3 Rail Defects
Rail-defect detection is an important factor in safeoperation of railroads. Rail defects develop fromservice use and are classified as transverse fissure,compound fissure, detail fracture, engine-burnfracture, horizontal split head, vertical split head,crushed head, piped rail, split web, head and webseparation, bolt-hole crack, broken base, rail weldfailures or defects, and damaged rail. However,because of improvements in rail design, manufac-ture, and maintenance practices, the number of raildefects that develop is remarkably small. Most ofthe rail defects that do develop are in the head orweb within the joint-bar area. Rail-defect-detectionequipment is available with which such defects cangenerally be detected. It makes possible removal ofdefective rail before a service failure occurs. Seealso Art. 19.14.1.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Rail-defect-detector cars are available that travelover the track at testing speeds of 6 to 15 mi/h. Byutilizing electrical magnetism or ultrasonic waves,equipment on board is able to locate internaldefects in the railhead. Ultrasonic equipment isused to detect defects in rail webs, particularly atrail joints, inside road crossings and other pavedareas, and in frogs. Most rail in main-line track inthe United States is tested once a year or more oftenwith detector cars.
19.14.4 Railroad Tie Renewals
Two methods are used for rail and tie replace-ments. The spot renewal method is used when onlya few scattered ties or rail sections need to bereplaced. Small gangs with limited equipment,such as boom trucks or backhoes, perform thiswork. Out-of-face renewals are used when largevolumes of ties or continuous rail sections arereplaced. This work is typically done with largegangs with many pieces of specialized equipment(see Article 19.14.6).
As rail on curves generally wears out before railon tangents, often rail replacements just involvecurve rail. Depending on the condition of the rail,the outside or high side rail may be replaced withnew rail and then reused on the inside or low rail.The low rail may then be scrapped or reused insidings or yards. Some tie renewals may be tied totrack surfacing cycles as the combined cost isusually less than if the work is done separately, dueto the cost of ballast and surfacing required for justtie renewals.
19.14.5 Structures Maintenance
At least annually, a detailed inspection shouldbe made of all bridges, trestles, and culverts.Structures with deficiencies should be rated withrespect to safe load-carrying capacity, whileappropriate safety measures are in effect to allowmovement of trains. This inspection should alsoestablish maintenance requirements or replace-ment options. Special investigations, such asunderwater inspections or detailed structural in-spections, may be performed on an as-needed basisor as specified by the railroad’s policy. Work not ofan emergency nature, such as cleaning and paint-ing, repairing concrete deterioration, and replace-
ment of any parts, should be scheduled. Periodicinterim inspections noting the condition of bridgesand trestles should be made at every opportunityin accordance with the railroad’s policy. Structuressusceptible to scour at the footings should beinspected more frequently. Patrolling and inspec-tion of bridge and drainage structures may berequired during storms and periods of high waterlevel and after earthquakes. Recommended inspec-tion practices are detailed in the “Manual ofRailway Engineering,” American Railway Engin-eering and Maintenance of Way Association.
Also, railroad buildings should be inspected todetermine if maintenance and repair requirementsare being met. Records of all inspections should bemaintained, as required by the railroad. Computersystems for management of structures may beutilized to assist in decision making and planning.
19.14.6 Mechanized WorkEquipment
When rails or ties are replaced out-of-face,mechanized equipment is available for handlingalmost every item or work. Mechanized, on-trackequipment such as spike pullers, power wrenches,tie-adzers, tie removers, scarifiers, tie installers,rail cranes, spikers, track liners, tampers, ballastregulators are utilized in arranged sequences toremove and replace rail, remove and install tiesand maintain track surface. There are also fullproduction machines that can changeout both tiesand rail in one continuous operation.
The rail-transportation engineer will find ithelpful to have available a copy of the “Pocket Listof Railroad Officials.” This is published quarterlyby Commonwealth Business Media, Inc., 400Windsor Corporate Center, 50 Millsbury Road,Cranbury, NJ 08512. It contains an alphabeticallisting of all railroad equipment supplies with thenames and addresses of companies that manufac-ture or sell these products.
19.14.7 Track Safety Standards
Legislation was passed by the U.S. Congress in1970 requiring the Federal Railroad Administrationof the Department of Transportation to establishtrack safety standards and to see that the railroads
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
complied with them. These standards establishedby the FRA prescribe minimum standards for thesafe operation of trains with regard to drainage,vegetation, ballast, rail defects (including endmismatch and end batter), welds, joints, tie plates,spikes, shims, switches, frogs, track appliances,deviations and variability in track geometry (runoffof elevation, alignment, cross level, and surface),maximum elevation on curves, maximum un-balance on curves, and track inspection. Thestandards have been established for differentclasses of track, classification being determinedby a range of permitted operating speed. Thesestandards are revised as the FRA considersnecessary or desirable and are issued as Title 49Transportation, Code of Federal Regulations, Part213 (49 CFR 213). The most recent revisionsoccurred in 1998. A volume including these andother railroad safety regulations is publishedannually. (Superintendent of Documents, Govern-ment Printing Office, Washington, DC 20402.)
19.15 Freight Terminals
On most railways, one or more yard facilities arerequired. Such a facility should have a receivingyard, classification yard, hold and repair tracks,engine servicing house, and departure yard(“Manual for Railway Engineering,” AmericanRailway Engineering and Maintenance of WayAssociation). Freight railroads should provide, inaddition to the normal yard tracks, through tracksfor trains that require minimal handling or donot require separating. The through tracks shouldbe located to meet requirements for AmericanAssociation of Railroad inspection, to accommo-date change-train crews, and to allow trains toproceed with a minimum of delay. In some cases,such tracks have permitted a reduction in thenumber of yard tracks required for handling oftrains.
A yard consists of a series of parallel tracks,called body tracks, on which cars are placed, andladder track usually at each end. A turnoutconnects each body track to a ladder track. Thus,the ladder track is a means of placing cars on orremoving them from each body track.
The receiving yard should be convenientlyaccessible from the main line, and its tracks should
be long enough to hold the longest train withoutdoubling (splitting) it into two tracks. The numberof receiving tracks required depends on thespacing of train arrivals and time required forclassification. A spacing of 18 ft should be providedbetween parallel ladder tracks, 15 ft between aladder track and any parallel track, and not lessthan 14 ft between body tracks. Additional clear-ance may be required, depending on car-inspectionneeds and other requirements, such as car cleaningor repair operations. A gradient of not more than0.15% is desirable to prevent the cars from rollingwithout setting the brakes.
The classification yard may be a flat yard if thenumber of trains and amount of switching arerelatively small. A gravity or hump yard should beused otherwise.
A hump yard utilizes gravity to expediteswitching of cars. The train of cars is pushed upan incline to a hump, at which point one or morecars are successively uncoupled while moving andallowed to roll down the incline from the humpinto the classification yard. The height of the humpmust be sufficient to impart enough velocity toovercome the rolling resistance of each car to thefarthest point in the yard. Thus, if the distance fromthe hump to the farthest point is 3000 ft and therolling resistance of the slowest-rolling car underadverse weather conditions is 10 lb/ton, equivalentto a 0.50% grade, then a minimum hump height of15 ft would be required. Another requirement isthat the decline from the hump be steep enoughand long enough to separate the cars sufficiently topermit operation of switches and to clear theswitches ahead of the following car. Usually, thehump height is from 16 to 20 ft. Two or three sets ofretarders are provided for controlling the speed ofthe cars into the classification tracks. The retardersare set so that each car will roll the desired distanceand couple to a standing car without undesirableimpact (up to 4 mi/h).
Humping speed is about 1 mi/h. In a fully auto-mated, or so-called push-button, yard, the operatorpushes a button numbered to correspond to thetrack number into which a car is to go. When thecar is uncoupled, it rolls down the hump and isweighed, if desired, on an electronic, uncoupled-in-motion, track scale. Also, the car’s rolling resist-ance is measured by determining change in speedover a given length of track. This information goesto a control computer.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
The approximate wheel load is measured by atrack scale device. This reading goes to the com-puter, to limit the amount of retardation so that thewheels will not rise out of the retarder. The carspeed is measured as it approaches each retarder,and this information goes to the computer. Whenthe operator pushed the button for the tracknumber, the computer was fed the total rollingresistance to the farthest point in that track. Awheel trip on each track corrects this value for thedistance taken up by the number of cars that havealready been placed in that track. From all thesedata, the control computer determines the speedthe car should have as it leaves the last retarder toroll to the desired point and retards the car to thatspeed. Usually, a radar device is used to measurecar speed. Retarders are pneumatically poweredbut electrically controlled. Switches are electricallyset by the computer for the track number punchedfor the car.
The body tracks of a hump yard typically have aslight downgrade on the incoming end and a slightupgrade on the leaving end, giving them a bowlshaped profile. This profile assists in slowing andstopping the cars within the yard.
The departure yard should be long enough toaccommodate the longest train and should belevel, if possible. If the grade is adverse to thedirection of starting, it should be at least 20% lessthan the ruling grade over which the train willoperate. Track spacing should be the same as forthe receiving yard.
Car-repair tracks should be provided toaccommodate the number of cars to be repairedand the repair time. These tracks can be alternatelyspaced 18 ft and a width sufficient to accommodatemechanical equipment. A paved driveway of railheight should be provided between tracks. It isdesirable to have a car-repair building, with therequired number of tracks, through which cars canbe moved by cables and “rabbits.” This providesmore efficient working conditions and mechanicalequipment for repair work at minimum cost anddelay. Some repair facilities employ a large truck-mounted vehicle as a car mover or a rubber-tiredvehicle with rail wheels to move cars in and out ofthe shop.
Most railroads do major service and repair oflocomotives at facilities that are centrally locatedon their system. These central engine houses orshops have platforms at cab floor height and
provide access to the top of the locomotive. Theyalso have below rail pits for access to the undersideof locomotives. Engine servicing at most yards islimited to minor repairs, cab cleaning and resup-plying of fuel, sand, water and lubricants. Allfacilities should provide means to collect and treatany spills of fuel or lubricants.
Other terminal facilities that may be required are:
Team tracks having an adjoining paved area forloading from trucks into the cars.
Mobile cranes for loading and unloading piggyback(truck trailers on flatcars) or containers on flatcars.
Stub tracks with a ramp at the ends. Narrow, car-floor-height platforms, with electric power outlets,should be placed between the tracks for loadingand unloading piggybacks.
Elevating-type inclines for end loading of auto-mobiles on auto-rack cars.
House tracks at the freight-station building for less-than-carload shipments.
Docks for loading cars or contents on boats.
Car dumpers that turn upside down and emptyhopper-type cars.
Stockpiling facilities for coal and ore. Storage binsand elevators for grain.
Provision of overhead cranes, wheel grinders,wheel drop pits, paint shops, wash houses, sani-tary-waste facilities for passengers, locomotives,and cabooses, industrial-waste facilities, and otheraccessories depends on the extent to which repairswill be made at the particular facility.
19.16 Passenger Terminals
Passenger terminal and station requirements varywith the type of passenger service provided.
19.16.1 Intercity Terminals
These comprise facilities for handling passengersand baggage and for servicing passenger carsand locomotives. The passenger facilities shouldinclude parking for automobiles, loading and un-loading areas for taxis and buses, ticket windows,waiting rooms, baggage check room, concessions,
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
food services, rest rooms, public telephones, andwalkways, stairs or escalators and elevators to trainconcourses.
Tracks should be on 20-ft centers, with pavedplatforms between. The platforms should becovered with a suitable type of roof. A minimumwidth of passage for passengers of 6 ft should beallowed on platforms, stairways, and ramps. Theincline of ramps should not exceed the maximumslope required for access by handicapped personsor as restricted by local building codes. Platforms atservice points for trains passing through shouldhave water hydrants, electrical outlets, steamconnections, and brake shoes available. Handlingof baggage, mail, and express requires separateplatforms or wide platforms so that trucks maypass without interfering with passengers; ramps orconveyor belts; and adequate space for sorting andtransferring to other trains or trucks.
Servicing of locomotives and cars requires acoach yard, preferably with a mechanical washer towash all equipment as it enters the yard. Tracks inthis yard should be level and on 20-ft centers. Theyshould have concrete platforms between them. Aninspection pit 36 in wide and 38 in below top of railis desirable for some of the trackage. Preferably,this area should be covered over to facilitate workin bad weather. Jacking pads and wheel drop pitsshould be provided. Other facilities needed arewater hydrants meeting U.S. Public Health Servicerequirements; hot water; low-pressure air connec-tions for cleaning; high-pressure connections for airbrakes; electrical service outlets, including 220-Valternating current for air conditioning equipment;steam supply lines; adequate lighting for nightoperation; a convenient supply of brake shoes andmounted car wheels; car pullers; commissaryfacilities for dining cars; service building providingoffices, toilet, wash, locker, and lunch rooms;storehouse; repair shops; refuse disposal; fireprotection; bottling plant for refilling gas cylinders;and fuel oil and sand supply for locomotives.
The extent to which all these facilities should beprovided depends on the number of trains andpassengers to be handled during peak periods,with an allowance for train delays. Detailedrecommendations related to the number of pas-sengers handled are in “Manual for RailwayEngineering,” American Railway Engineering andMaintenance of Way Association (AREMA), 8201Corporate Drive, Suite 1125 Landover Maryland20785 (www.arema.org).
19.16.2 Commuter Terminals
These should provide most of the facilities listedfor passenger terminals, except for a baggagecheckroom and food services which would prob-ably not be needed. Vending machines may pro-vide some food service.
Rapid-Transit Terminals n Requirementsfor stations are given in Art. 19.6. Terminalfacilities should be provided at the end of eachline for car storage, and a shop should be availablefor emergency repairs. A shop for overall andscheduled maintenance of cars should be providedat the location most suitable from the standpointof accessibility in operation, land availability, en-vironmental factors, and so forth.
For storage tracks, the length required may bedetermined by calculating the length of the numberof cars required for peak movements plus 10% forspare units to replace cars out of service for repairs.Storage tracks shouldbe level, andgrade for leadandother tracks should not exceed 0.3%. Curves shouldnot be less than 200-ft radius but should be flatter ifthe car units are designed to require a longer radius.
One or more shops should be provided at thechosen shop location for repair of electrical, elec-tronic, hydraulic, pneumatic, control, and undercarequipment (including drop pits); for mechanicalrepairs; for wheel grinding; and for painting andseat repair. An automatic car washer should beprovided. It is desirable that all the above workareas, except the car washer, be located undercover; work should be scheduled on an assemblyline basis; all work should be automated; and allworkers should be provided with power tools tothe extent such tools are available.
Storage and shop areas should be surroundedby a suitable fence to prevent trespassers fromentering, for safety and to avoid pilferage. A guardor automatically operated gates should guard theentrance tracks and driveway to the storage andshop area. A 7-ft-high chain link fence with barbed-wire outriggers inside the right-of-way is well-suited for this purpose.
19.17 Station Location andCharacteristics
Station locations have already been established inthe United States for passenger trains and existing
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
commuter and rapid-transit service. Manyexisting stations, however, are being remodeledor replaced to satisfy Federal laws requiring accessfor handicapped persons and for other safetymeasures. Commuter stations are located insuburbs or city areas a few miles apart, and wherelocal or bus street transportation generates a largeenough volume of passengers to justify a train stop.Usually, not all commuter trains stop at all thestations but a schedule will be established to pro-vide reasonably frequent service, particularly inmorning and evening rush hours, at stations withrelatively low traffic volume.
19.17.1 Stations for Rail Transit
When a new system is being planned, severalfactors should be considered in deciding stationlocations:
Physical constraints: available space for thestation, space for parking, space for bus andautomobile circulation.
Accessibility: convenient location within networkof freeways and arterial and feeder bus routes.
Service potential: number of persons, households,students, and jobs of various types located within700 ft, 1500 ft, and 3000 ft of each station. Mostpeople living or working within 1500 ft of a stationwill walk to or from it. In outlying, low-densityareas, automobiles and feeder bus lines willexpand the service area of a station.
Convenience to major institutions and centers:schools, hospitals, recreational areas (includingsports facilities), and major industrial and com-mercial concentrations located within 700 ft of eachstation.
Development opportunities: joint development po-tential of vacant or deteriorated structures within700 ft of each station.
Impact on neighborhood: localized traffic conges-tion, reinforcement of community centers andboundaries, and conformance with local develop-ment plans.
Projected ridership: number of riders coming toand from each station, projected for 15 to 25 yearsahead, depending on transportation planningrequirements. Passenger-seat-mile (1 passengermoving 1 mi) provides a useful measure for costcomparisons between the different modes of travel.
From the above, it will be possible to determinefor each station the location (tentative) that willattract the maximum number of riders and give the
best service. Stations should be placed closertogether in areas expecting the greatest number ofriders, not only to give better service but to avoidundue congestion within and outside the station.
19.17.2 Station Platforms
These should be as long as the longest train thatwill be operated. For passenger and commutertrains, the platforms or paving for loading andunloading are generally outside the track or twotracks. Also, most existing platforms are at top-of-rail level and 6 ft or more wide. However, in newconstruction for commuter service and rapid-transit service, platforms along or between tracksshould meet the height required by the rollingstock selected andmeet the requirements for accessby handicapped persons. Platform height mayrange from rail level to as much as 42 in above therails. In subways, platform width should in no casebe less than 10 ft and should provide 8 ft2 ofoccupancy space per person for maximum assem-bly crowds. In one subway system, a platformbetween tracks about 30 ft wide is provided. For at-grade systems, an existing sidewalk or ramp thatmeets building-code requirements may be utilizedto provide access to the trains, depending on thetype of car.
19.17.3 Provisions for Circulationin Stations
Important criteria, in addition to all appropriatesafety measures, are traffic-handling capability,consistently available information, and orientation.Maps of the system showing all lines and stationstops should be placed conspicuously, with theparticular station clearly designated thereon. Sta-tions should include a free area and a service area.Provision should be made for concessions, if any, inthe free area and necessary facilities, such as electricoutlets, water supply, and so on should be providedat a suitable location for the concessions. Automaticcoin-operated dispensers should be located in thefree area, but both these and concessions should belocated so as not to interfere with circulation ofpassengers to and from the trains.
A minimum clearance of at least 8 ft should beprovided throughout the station and platform tomeet the requirements of the equipment used.Adequate space should be provided at ticket
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
facilities to allow for a line of ticket purchaserswithout interference with the normal flow ofpassengers.
Passageways, stairs, ramps, and areas forhandicapped persons should be located to providebalanced train loading and unloading—usually ateach end of the platform, or at the platform mid-length, or both. An island-type platform betweentwo tracks is preferable to a platform on each sideof the two tracks.
To determine the space required for exit andentrance doors, which should open out or revolve,the maximum number of passengers that will passin any 15-min peak period should be estimated.Enough space should then be allowed to clear theplatform under normal conditions within theheadway time between trains. For emergencyevacuation of a train, provision should be madeto clear the platform in 4 min. To do this, thedesigner may assume a crush capacity of 25passengers per minute per foot width of passage-ways, 20 passengers per minute per foot width ofstairways, and 100 passengers per minute for each48-in escalator. Enough supplemental stairwaywidth should be provided to permit evacuation ifthe escalator should become inoperable.
Telephones, toilets, storage lockers, servicerooms, and toilets for station personnel should beprovided at stations as warranted.
Wherever steps are utilized for access, a ramp,lift, or elevator must also be provided for access forpersons with disabilities. Access should be illumi-nated when required for safety. Steps and rampsshould be kept clear or sanded where exposed tothe weather, and handholds meeting building-coderequirements should be provided on both sides. Allwalking surfaces on stairs and in passagewaysshould be kept dry and covered with a suitablenonskid material. Small sidewall depression“trenches” parallel to the side walls and suitablydrained should be provided to accomplish this.
Escalators should be provided to carry passen-gers up whenever the stair height exceeds 12 ft andto carry them down when it exceeds 24 ft.
19.17.4 EnvironmentalConsiderations in StationDesign
Station construction should comply with the ap-plicable building codes. Suitable lighting, satisfac-
tory noise level, comfortable air conditioning,pleasant appearance from the standpoint of bothdecor and cleanliness, control of wind and odors,and clear circulation (by appropriate directionalsigns if needed) should be provided.
Lighting is of great importance for safety andthe security of passengers. Table 19.5 is a guide forminimum illumination levels at different locations.Signs at street level, illuminated at night, shouldindicate clearly where the rapid-transit entrance,station, or stop is located. Steps up or down to thestation should also be illuminated when requiredfor safety.
Subway Ventilation n Objectives are to:
Provide a comfortable environment for patronsand staff.
Table 19.5 Recommended Minimum Illumina-tion Levels in Passenger Stations*
LocationsIllumination,foot-candles
Platform, subway 20Platform, under canopy,surface and aerial
15
Uncovered platform ends,surface
5
Mezzanine 20Ticketing area, turnstile 30Passageways 20Stairs and escalators 25Fare-collection kiosk 100Concessions and vendingmachine areas
30
Elevator (interior) 20Above-ground entry tosubway (day) 30
(night) 10Washrooms 30Service and utility rooms 15Electrical, mechanical, andtrain-control equipmentrooms
20
Storage areas 5
* From “Guidelines for Design of Rapid Transit Facilities,”American Public Transportation Association.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Provide, in the event of fire, control and removal ofsmoke and a supply of fresh air for evacuation ofpassengers and for fire-fighting personnel.
Provide for the removal of heat generated bynormal train operation.
Provide control of condensate and haze andremoval of objectionable or hazardous odors andgases.
The piston action of trains will provide aconsiderable amount of ventilation if suitable ventshafts are provided. If necessary, supplementalmechanical ventilation must be provided. Maxi-mum piston-type ventilation can be obtained byhaving the tunnel or subway section as near the sizeof the train cross section as clearance requirementswill permit and having a separate tunnel orsubway for each track. Fan shafts must be locatedrelative to the vent shafts and stations in such away as to ensure that all sections of the subway andstations can be purged under emergency con-ditions. The ventilation rate should satisfy thepurge rate. A minimum air velocity of 4 ft/s isrecommended for determining the sizes of fans andappurtenances. Vent and other shaft openings onthe surface should be located to draw in unpollutedair and protected by gratings or screens. Acoustictreatment of the shafts should be provided ifneeded. Fans for emergency ventilation should beconnected to power feeders from two separatesources and should be operable through remotecontrols located at a control station.
(“Subway Environmental Design Handbook,”vol. 1, Federal Transit Administration, Washington,DC 20590.)
19.17.5 Security andCommunications
Security can best be provided by closed-circuittelevision cameras suitably located at strategiclocations in the station, passageways, and plat-forms. These instruments should be monitored ateach station at which there is an agent and at acentral control station. An alternative for trainswould be to have the monitors for the cars wherethe train attendant can see them and provide theattendant with a means of communicating with thenearest agent and the central control office.
Telephone communication between each stationand the central control office should be provided.
Portable radios or mobile telephones should beconsidered for use between security personnel andstation agents and the central control office. Thistype of communication is not effective in subwaysor tunnels, so its provision to train attendants willdepend on how much of the line is open or aerialstructure. Or a special antenna line can be placedthrough the subway and tunnel sections to enableportable communication.
19.17.6 Fare Collection
This is generally accomplished on the trains incommuter service but at the stations in rapidtransit. For this purpose, station personnel can beaugmented by turnstiles, either coin-operated orusing coded tickets or some other suitable method.In some commuter and rapid-transit service, coin(or currency or coin) vending machines are usedfor selling coded tickets, and computer-controlledturnstiles are used for collecting and monitoringthem. Several transit systems allow customers topurchase tickets and do not use turnstiles orcollection systems. The success of such methodsdepends on patrolling and customer honesty. Somesystems establish a central zone with free travelbut exact graduated fares with distance away fromthat zone. One system has experienced about150 failures a month with 43 changemakers andwell under the one-failure-per-machine-per-monthguarantee for its computerized turnstiles.
19.17.7 Tracks between SubwayStations
Between subway stations, tracks usually are sep-arated by the tunnel walls or a concrete wall.Walkways with a minimum width of 2 ft should beprovided on one side of all line sections of tunnelsand subways, and for high-speed train operation, ahand rail should be placed on the wall 3 ft abovethe walkway floor. Walkways should be placed onadjacent sides of the wall to permit cross connec-tion between the walkways. Crossways should beplaced not more than 1000 ft apart for workers andemergency evacuation of passengers.
(“Guidelines for Design of Rapid Transit Facili-ties,” American Public Transportation Association,1666 K Street NW, Suite 1000 WA, DC, 20006,(www.apta.com).)
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
19.18 Vehicles for RailTransportation
Except PRT cars, vehicles predominantly use steelwheels on steel rails because of the low rollingresistance and heavy weight that can be supportedon a single wheel. A few rapid-transit systemsutilize vehicles with rubber tires that run onconcrete beams or “rails” and are self-guided.Disadvantages of such vehicles are the higherrolling resistance, greater operating cost, and lowerweight-supporting capability. Another disadvan-tage of the rubber-tired system occurs in operationthrough turnouts. In one system (Fig. 19.18), therubber tires are spaced far enough apart to permit aregular rail track structure with switch points andfrog to be placed at the turnout location. Thevehicle has two steel wheels and an axle at eachend. As the vehicle approaches the turnout, theconcrete rails are ramped downward so that thevehicle is supported on the steel wheels throughthe turnout, after which the concrete rails areramped up to support the vehicle again. Vehiclesmust be operated at slow speed through theturnouts in this type of rubber-tired system.
PRTsystems are designed for a specific purpose,and a type of vehicle is used that best serves thatpurpose. Mostly, these systems are used fortransferring passengers at airports or in recreationcenters. Rubber tires are preferred, partly becausethey provide traction for grades as steep as 10%. If
the guideway is exposed to snow or ice, therunning surface for the tires must be heated in coldweather. Magnetic levitation support is also beingconsidered. Passenger capacity per vehicle variesfrom 4 to 20 seated. Mostly vehicles are operated assingle or double units, but some operate in five- toeight-car trains.
19.18.1 Method of Traction
Trains for rail passenger and freight intercitysystems are primarily moved by diesel-electriclocomotives. Where traffic density warrants,electric locomotives are used with an overheadcatenary or a third rail. Most commuter systemsare powered by diesel-electric locomotives withpush-pull controls in some of the cars so that thetrain does not have to be turned around at eachterminal of the run. Several commuter systemsare electrified, and each car has its own motordrive so that a separate locomotive is not required.All rail-transit systems are electrified, and each carhas a driving motor for each axle to give sufficientadhesion for the rapid acceleration and decelera-tion required. Personal rapid-transit systemsare also electrified. Some PRT systems, however,are propelled by linear induction motors set atintervals along the guideway. Propulsion isachieved with reaction plates on the bottom ofthe vehicles. Research sponsored by FTA on PRTsystems includes the following guided minivehicle
Fig. 19.18 Cross section of guideway and vehicle for Paris Metro rubber-tired rapid-transit vehicles.Steel rails and wheels are required for guidance through turnouts.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
systems: suspended monorail, air levitation ona concrete guideway, rubber tires on an alumi-num guideway, and rubber tires on a concreteguideway. No doubt other systems will bedeveloped.
Since switching is such an important part of apersonal rapid-transit system, the conventionaldual-rail wheel system has an important advantagethat will be difficult but not impossible toovercome. For example, the people-mover vehicleshown in Fig. 19.19 is supported on rubber-tiredwheels and guided by another set of rubber-tiredwheels bearing on a steel guide beam. Forswitching, one end of the guide beam can bemoved back and forth to line up with the desiredtrack. The personal-rapid-transit car in Fig. 19.20 is
supported on four rubber-tired wheels and guidedin the guideway by another set of four rubber-tiredwheels. The guide wheels may be computer-controlled to make the vehicle follow either the leftor right guiding surface. Thus, at a station, the carmay be made to pass by directing the guide wheelsto follow one guiding surface, or the car may bemade to turn into the station track for a stop bydirecting the guide wheels to follow the otherguiding surface. No moving parts are needed inthe guideway to make a car bypass or stop at astation.
Supports for any type of system can be wheels(steel- or rubber-tired), air-cushion levitation (Fig.19.21), or magnetic levitation (Fig. 19.22). Sinceeither type of levitation is costly and complicated,
Fig. 19.19 Cross section of guideway and vehicle for Westinghouse people-mover system.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
there must be overriding advantages to justify thisexpense if such a system is to be used.
Power for a transportation system can bediesel-electric, electric, gas-turbine electric, gas-turbine hydraulic, jet propulsion, linear inductionmotor (Figs. 19.21 and 19.22), or pneumatic. Thecosts and characteristics of each must be takeninto account in selection of the type of propulsionfor any given transportation system. There hasbeen much experience with the diesel-electric andelectric motor drives; there has been someexperience with the gas-turbine electric motorand gas-turbine hydraulic drive. This experienceshows that it is difficult to compete with the
diesel-electric or the electric motor drive. So far,the efficiency of the turbo-electric or turbo-hydraulic drive has not been brought up to thatof the other two.
For speeds over 100 mi/h, the electric motordrive has an advantage over the diesel-electricbecause the electric drive does not have to pull theweight of the electric generating plant; also, forshort periods of time, it can draw a great deal ofpower from the catenary, whereas the diesel-electric has a fixed maximum power.
A speed of over 200 mi/h has been attained intrial runs with an electric-motor-powered vehiclesupported on steel wheels on conventional track.
Fig. 19.20 Outline diagram of Boeing personal-rapid-transit system with single, elevated guideway atthe University of West Virginia, Morgantown, W.V. Vehicles accommodate 8 seated and 13 standing.Speed ranges up to 30 mi/h. During peak hours, this system operates on a scheduled basis; otherwise, on apassenger-demand self-service basis. Tire running surfaces are heated to melt snow or ice.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
However, to attain speeds of 200 to 300 mi/hregularly, vehicles may have to be powered by alinear induction motor or turbine jet. The latter,however, may be objectionable because of the noiselevel, and the former poses the difficulty of keepingthe track reactor in accurate line and surface forsuch high speeds, as well as maintaining it freefrom windblown debris, sand, snow, and ice. Atsuch speeds, the power required to overcome airdrag is considerable.
19.18.2 Levitation Systems
Since 1965,much research, development, and testinghave been conducted in the United States, Great
Britain, Germany, France, Japan, and Canada onlevitated transportation systems. Two concepts havebeen studied: the tracked air-cushion vehicle (Fig.19.21) and themagnetic levitationvehicle (Fig. 19.22).The air-cushion support system is not favored bymany engineers working in the levitation fieldbecause of its high noise level, power requirements,weight of the air-cushion fans and motors, and lackof a suitable design for track switches.
One specialist states that a high-speed levitationsystem should offer these advantages: reducedtravel time, comfort, safety, punctuality, competi-tive fares, minimum disruption of the environ-ment, compatibility with other transit systems, anda minimum chance of failure. To these factorsshould be added the condition of being operable inall weather conditions.
The most promising type of magnetic levitationsystem requires no electric-current pick-up systembetween guideway and vehicle. Magnetic levita-tion supports the vehicle. For this purpose, three-phase alternating current is fed into coils located inthe guideway and propels the vehicle. Levitation iscontrolled by changing the voltage of the magnets,and speed is controlled by changing the frequencyof the three-phase winding. Speeds in the range of250 to 300 mi/h appear practical of attainment,with an energy consumption per passenger-milesomewhat less than that of an airplane traveling500 mi/h and somewhat more than an automobileat 60 mi/h.
Figure 19.23 shows a schematic of such amagnetic levitation system. The guideway may beelevated for practical reasons, although it could beplaced underground. This system offers manyadvantages: no direct electrical or mechanicalcontact with the vehicle; no guiding, support, orpropulsion friction; no moving parts to wear; highreliability; good passenger safety; low noise level;exceptional passenger ride comfort; and no atmos-pheric pollution. Indications are that its first cost aswell as operating and maintenance costs can becompetitive.
Of particular interest to civil engineers in thissystem are the construction of the guideway andsupporting piers (or tunnels), the maintenance ofthe guideway alignment and surface, and obstruc-tion warning devices.
Although levitation of the vehicle is generallyassociated with use in high-speed service, a PRTvehicle with magnetic suspension and linearpropulsion that is used for slow speed and frequent
Fig. 19.21 Schematic illustrating the principleof tracked air-cushion vehicle with vertical reactionrail for linear induction motor.
Fig. 19.22 Schematic illustrating the principleof the magnetic levitation vehicle with horizontalreaction rail for linear induction motor.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
stops has been developed by Automated Trans-portation Systems, Boeing Aerospace Company.
(R. D. Thornton, “Flying Low with Maglev,”IEEE Spectrum, April 1973; Gerhart W. Heumann,“German High-Speed Railroads,” Machine Design,Sept. 6, 1973; Klaus-Glatzel, G. Khordok, andD. Rogg, “The Development of the MagneticallySupported Transportation System in the FederalRepublic of Germany,” Transactions on VehicularTechnology, vol. VT-2, no. 1, February 1980, Instituteof Electrical and Electronics Engineers, 345 E. 47thSt., New York, NY 10017.)
19.18.3 Freight Cars
General types of freight cars include flat, box, stock,tank, hopper, covered hopper, gondola, refriger-ator, and caboose. Some special types of freight carsinclude trailer on flat, double-stack container cars,auto rack, auto pack, container on flat, steel sheet,steel coil, and Hy-Cube. The objective of specialcars is improved service; for example, auto-packcars completely enclose the automobile andprevent the damage and pilferage that frequentlyoccur with open auto-rack cars. Schnable carsare used to carry specially heavy and wide loads.The auto train combines auto-rack cars to transportthe automobiles of passengers and conventionalpassenger cars of different types to transport
the passengers. The coupled length of freight carsranges from 24 ft for ore hopper cars to 94 ft forHy-Cube boxcars.
For freight cars to be freely interchanged in theUnited States, Canada, and Mexico, many com-ponents must have Association of AmericanRailroads approval. These components includecouplers, draft gear, center sill, air-brake system,wheels, axles, bearings, truck side frames, springs,snubbers, bolsters, and side bearings. The total railload that is permitted is determined by the journalsize. Table 19.6 lists maximum loads for severaljournal sizes for a car having four axles.
Width and height of freight cars must comewithin Plate B (Fig. 19.24) for unrestricted inter-change and Plate C for interchange on most roads,as given in AAR Mechanical Division Specifica-
Fig. 19.23 Schematic of high-speed, magnetic levitated system developed for the Federal Republic ofGermany by Transrapid EMS. (a) The vehicle levitation and propulsion system; (b) the guideway andsupport pier. Piers are spaced 25 m center to center.
Table 19.6 Maximum Permissible Freight-CarWeight per Rail
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
tions for Design, Fabrication, and Construction ofFreight Cars. The dimensions of Plate B for widthmust be reduced for cars having truck centers inexcess of 41 ft 3 in.
Most railroads have a clearance bureau forverifying load clearances and routes for carscarrying freight that exceed Plate B and Plate Climits. In addition, heavy loads that exceed weightrestrictions are also cleared but restricted todesignated routes and speeds, especially whentravel over structures is necessary.
Freight cars of 45-ft coupled length can beoperated around 458 curves coupled together.
Boxcars of 94-ft coupled length coupled to a shortcar can be operated around a curve of about 208.Curve negotiability depends on clearance of the carcorners and the free angling of the couplers in thedraft gear pockets. (“Car and Locomotive Builders’Cyclopedia,” Simmons-Boardman Publishing Cor-poration, Omaha, Neb.)
19.18.4 Passenger Cars
Types of passenger cars include baggage (baggage-dorm), coach, diner (cafe, dinette), lounge (club,parlor), sleeper, and combinations. Dimensions ofpassenger cars adopted as recommended practiceby the Association of American Railroads (AAR)Mechanical Division are: coupled length, 85 ft;width, 10 ft; height, 13 ft 6 in (bi-level cars, 16 ft6 in); and truck centers, 59 ft 6 in. Weight of thesecars empty ranges from 100,000 to 160,000 lb.Seating capacity ranges from 44 to 89 in coachesand 23 to 48 in food service cars.
According to information provided by AM-TRAK, a sleeping car has various combinations,mostly 10 roomettes and 6 bedrooms; a slumber-coach has 24 single roomettes and 8 doubleroomettes. (The “Car and Locomotive Builders’Cyclopedia,” Simmons-Boardman Publishing Cor-poration, Omaha, Neb., contains photographs andfloor plans of the latest passenger cars built.)Passenger cars must be constructed to meet AARrequirements for safety and interchange. Four-wheel trucks are generally used with 36-in-diameter wrought-steel wheels, roller bearings,helical or air-coil springs, snubbers or shock absor-bers, cross stabilizers (lateral bumper), and loadequalizers. Passenger-type air-brake equipmentand air signal lines are provided. Electric air con-ditioning, heating, and lighting for the cars arepowered through train lines from the head end.
Passenger cars are designed to negotiate acurve of 250-ft minimum radius when coupledtogether.
19.18.5 Commuter Cars
Several types of commuter cars are in use. One typeis designed for push-pull operation by a separatelocomotive. It is of semimonocoque design ofaluminum with high-strength steel underframe.The vehicle is 85 ft long, 10 ft 6 in wide, and 12 ft8 in high above top of rail. Truck centers are 59 ft6 in, and wheel base is 8 ft 6 in. Trucks are inboard
Fig. 19.24 Plate B clearance diagram for freightcars for unrestricted interchange service. Carsmay be constructed to an extreme width of 10 ft8 in and to the other limits of this diagram whentruck centers do not exceed 41 ft 3 in. With truckcenters of 41 ft 3 in, the swingouts of end of carshould not exceed the swingout at center of car ona 138 curve. A car to these dimensions is definedas the base car. When truck centers exceed 41 ft3 in, the car width should be reduced tocompensate for the increased swingout at thecenter or ends of the car on a 138 curve, so that theextreme width of the car does not project beyondthe center of the track more than the base car. The21⁄2-in clearance above top of rail is an absoluteminimum. (Mechanical Division, Association of Ame-rican Railroads.)
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
bearing, air suspension, with 32-in-diameterwheels, eight composition brake shoes, and elec-tropneumatic braking. Weight is 74,000 lb. Seatingcapacity is 104. There are two 33-in-wide doors oneach side near the car ends. Loading is from lowplatform level.
Another type is the bilevel or gallery-type push-pull car. A typical car of this type is 85 ft long, 10 ftwide, and 15 ft 10 in high. It seats 161 passengers ina trailer car, 155 in a cab car. The cab car weighs128,500 lb; the trailer car, 123,400 lb. These cars arepulled or pushed in the train by a diesel-electriclocomotive. A cab car with controls for the engineeris located at one end, the diesel-electric unit at theother end of the train. As many trailer cars asneeded are coupled between them. These cars havefour-wheel trucks 59 ft 6 in on centers. Double ortriple doors at midlength of the cars expediteloading and unloading at low platform level.
A self-propelled rail diesel car is used to someextent in commuter service. A typical car is 85 ftlong, 10 ft wide, and 14 ft 7 in high. It has two four-wheel trucks 59 ft 6 in on centers. The weight is112,800 lb and seating capacity 89. A 550-hp dieselengine with electric drive powers the car. Thesecars are also used for mail, express, and passengerservice on lines having light traffic. Loading is fromlow platform level.
The fourth type of commuter car is the electricmultiple-unit (MU) coach. This type is used onlyfor high traffic density. One design of MU car is85 ft long, 10 ft wide, and 12 ft 6 in high. It has 59-ft6-in truck centers; trucks have two axles spaced 8 ft6 in on centers. The car weighs 105,600 lb and seats122 passengers. Generally, several units are used inone train, but each has its own catenary trolley andis powered by four 156-hp motors. Loading is fromfloor level.
A fifth type is a double-deck MU car with cabcontrols at opposite ends of adjoining cars. Thistype is 85 ft long, 10 ft 53⁄4 in wide, and 15 ft 10 inabove top of rail. Weight is 134,000 lb. Seatingcapacity is 156, equally divided between thedouble doors on each side near car midlength. Italso has a single door on one side at the cab end.It operates from a 1500-V dc catenary system. Thepantograph that collects the current for each car islocated in a roof offset at the cab end, measuring1 ft 10 in deep and 10 ft 49⁄16 in long. Loading isfrom floor level.
A sixth type of commuter car is constructed tooperate off the third rail in electrified territory and
from its own power supply in nonelectrifiedtrackage. These cars are built as pairs with onepower source. Each car is 85 ft long, weighs140,000 lb, and seats 240 in a “married pair” ofcars. Loading is from either floor or ground level.Power is supplied by two 550-hp gas turbine-electric generator units, mounted directly underthe roof for easy maintenance. The two gas turbinesdrive alternators providing three-phase power at420 Hz, 277 to 480 V. The rectified output istransmitted to a dc-dc chopper circuit that controlsseparately excited traction motors. The choppers(solid-state electronic switching devices) are ad-vanced means of controlling dc traction-motorinput power to provide smooth, efficient, jerklessacceleration for passenger comfort.
Electrically self-propelled commuter and rapid-transit cars may store energy developed byregenerative braking in storage batteries or in ahigh-speed flywheel for later use in train accelera-tion. This reserve energy supply could be used tooperate the cars to the next station in the event of apower failure and, with storage batteries, to movecars in and out of yard and shop tracks and thuseliminate the need to electrify this trackage (res-ulting in less cost and greater safety).
All the types of commuter cars describedpreviously have tinted glass windows, are airconditioned, and have comfortable seats, attractivedecor, good lighting, racks for luggage or apparel,and toilets.
19.18.6 Rail-Transit Cars
Essential characteristics of rapid-transit cars arerapid acceleration and deceleration, quick entranceand exit, maximum seating capacity, and passengercomfort. These are provided, respectively, by high-horsepower motors, a combination of dynamic andair brakes, and lightweight construction; severaldoors per car; loading and unloading at floor level;seats and arrangement designed for best spaceutilization; and padded upholstered seats, airconditioning, good lighting, and attractive decor.Table 19.7 gives comparable car data for severalrapid-transit systems. Cars can carry up to 350passengers. Seats provided range from 56 to 83.Figure 19.25 illustrates the type of cars used on theDenver Light Rail System.
The Bay Area Rapid Transit (BART) cars are agood example of car design that offers excellentservice, comfort, and safety. Type A cars have one
Length over coupler faces 75 fta 75 ft 0 in 55 ft 4 in 74 ft 918 in 75 ft 0 in 75 ft 0 inn
Height:Overall 10 ft 6 in 12 ft 11⁄2 in 12 ft 10 in 11 ft 111⁄2 in 10 ft 101⁄2 in 11 ft 10 inHeadroom 6 ft 9 in 6 ft 83⁄8 in
d 7 ft 4 in 6 ft 11 in 6 ft 10 in 6 ft 10 inFloor to top of rail 3 ft 3 in 3 ft 103⁄8 in 3 ft 10 in 3 ft 71⁄2 in 3 ft 4 in 3 ft 8 inWidth, maximum 10 ft 6 in 10 ft 0 in 9 ft 1 in 10 ft 4 in 10 ft 13⁄4 in 10 ft 6 inWeight, total less passengers 56,500 lbb 87,000 lbe 48,760 lb 55,500 lb 72,000 lb 76,000 lbo
Trucks:Truck center distance 50 ft 0 in 54 ft 0 in 38 ft 0 in 54 ft 0 in 52 ft 0 in 52 ft 6 inWheel diameter 30 in 34 in 28 in 28 in 28 in 34 inTrack gage 5 ft 6 in 4 ft 81⁄2 in 5 ft 21⁄4 in 4 ft 107⁄8 in 4 ft 81⁄2 in 4 ft 81⁄2 inWheelbase 7 ft 0 in 6 ft 10 in 6 ft 8 in 6 ft 10 in 7 ft 3 in 7 ft 3 inMinimum radius horizontal curve 500 ft 145 ft 140 ft 250 ftf 250 fth 350 ftMinimum radius vertical curve 1670 ft 2000 ft 3000 ft 2000 ft i 1.5%/100 ftp
Number of motors 4 4 4 4 4 4Horsepower per motor 150 115 100 116 160 160
Dynamic brake range 80–4 70–15 55–1 50–10 15 fade out 70–3Doors:Number per side 2 4 3 4 3 3Height 6 ft 4 in 6 ft 3 in 6 ft 3 in 6 ft 51⁄4 in 6 ft 4 in 6 ft 7 inWidth 4 ft 6 in 4 ft 2 in 4 ft 1 in 3 ft 9 in 4 ft 2 in 4 ft 2 in
Minimum number ofcars per train
2 4 2 2 2 1
Maximum number ofcars per train
10 8 10 6 8 8
aFor A cars; B cars ¼ 70 ft.bFor A cars; B cars ¼ 55,000 lb.cFor A cars; B cars ¼ 76dLow ceiling; 7 ft 23⁄8 in for high ceiling.eFor A cars; B cars ¼ 84,000 lb.fMinimum desirable for main-line box structure and circular tunnels ¼ 1000 ft.gHigh rate; low rate ¼ 1.9.hFor yard track; main line ¼ 500 ft.iParabolic, min. length ¼ (G1 2 G2) 100 ft, but not less than 200 ft.jOn 1% grade.kBelow 50 mi/h.lFor A and B cars; C cars ¼ 62.mFor A and B cars; C cars ¼ 235.nFor A and B cars; C cars ¼ 75 ft 4 in.oFor A and B cars; C cars ¼ 79,700 lb.pParabolic.qMaximum overspeed.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
slanted end with a cab for a single attendant fortrain control (when needed), automatic trainoperation sensors, and a communications system.A cars are placed with the slanted end at the frontand rear of the train, an arrangement that gives apleasing, streamlined appearance. As many B carsas needed, up to 8, are placed between the two Acars. Vinyl-padded double seats are placed on eachside of a middle aisle. The floors are carpeted;smoking is not permitted. The car interior is madeof simple, durable, and fire-resistant constructionand designed for ease of cleaning. No painting isrequired, and advertising signs are not used.Lighting fixtures use focusing lenses and provide30 to 35 fc at reading height, 20 fc at floor level. Attwo locations in each car, a small push-to-talkintercom set permits passengers to report emer-gencies or seek information from the attendant.Either the attendant or the central office can makeannouncements to passengers from speakers ineach car. A large enclosed passageway betweencars with biparting doors and large panes of glassallows passengers to see seats in adjoining cars.This also facilitates observation of two cars by theattendant during night hours.
Each car has its own air conditioning system,which provides draft-free, uniform air distributionwith fresh air infusion, 12-ton refrigeration, 30-Wheating, and humidity control to below 60%relative humidity.
Automatic train control and cab signals areprovided, but the attendant can override the traincontrol in an emergency. Automatic couplers com-plete 24 electrical circuits throughout the train.
Wheels are designed for light weight and noisereduction. They have AAR wrought-steel, heat-treated rims and aluminum hubs. The car supportand trucks include level-controlled air bellows,rubber “doughnuts” around the journal rollerbearings, and hydraulic shock absorbers.
A dc chopper is used to control the 450-V directcurrent to each motor to give smooth starting andstopping. An automatic car identification system isused, with color-coded labels on each car. Scannersare located on yard leads to record miles run formaintenance purposes and to determine thelocation of each car.
Communication between trains and centralcontrol is by radio, using a line antenna throughsubway sections.
Fig. 19.25 Typical light rail vehicle in service for the Regional Transportation District (RTD) inDenver, CO.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Amore detailed description of the BARTsystemis in “Modern Railroads Rapid Transit,” February1972; and “The Bay Area Rapid Transit VehicleSystem,” L. A. Irvin and J. R. Asmus, paper 680544,Society of Automotive Engineers.
19.18.7 Railway Service Cars
These are non-revenue and maintenance-of-waymaterial and equipment cars and other specialpurpose cars. Maintenance-of-way cars include airdump cars for carrying rip rap and embankmentmaterial, ballast cars, tie cars, car sets with racks forcarrying welded rail strings, clearance measuringcars, track geometry cars for measuring the qualityof the track under loaded conditions, and flangers,spreaders and rotary snow plows. Other specialtyequipment includes scale test cars, dynamometercars for testing locomotives and wreck trains thatcontain tool cars, track material and cars andlocomotive cranes of up to 250 ton capacity.
Instead of using wrecking cars, some majorrailroads employ contract services. The contrac-tors use construction equipment, including track-mounted machinery, modified to handle cars andlocomotives, to removed derailed equipment andrestore trackage. The contractors generally movetheir equipment by truck and trailer and useadditional trailers for cooking and sleepingfacilities.
19.18.8 Locomotives
In the United States, almost all freight and pas-senger trains are moved and switching operationsdone with diesel-electric locomotives. Less than1.5% of locomotives are electric; most of theremainder are diesel-electric. There are a fewlocomotives of other types in use, such as diesel-hydraulic and gas turbine-electric. Locomotivecapacity is based on the rated horsepower, tractiveeffort, and rail adhesion characteristics of thelocomotive. These determine the drawbar pullavailable for hauling cars.
Diesel-electric locomotives use on-board dieselengines to power electrical generators that feedcurrent to electric motors that drive the axles. Earlydiesel-electric locomotives used Direct Current(DC) electrical systems. New diesels use either DCor Alternating Current (AC).
Diesel-electric can be operated in multiple unitsby one engine-man to afford the horsepower and
tractive effort required. It requires relatively fewstops for fuel and water, and it has excellentstarting characteristics because all the weight is onthe driving wheels. In long unit trains, diesel-electric locomotives are used mid train and/or atthe end of the train as helpers.
An electric locomotive has good efficiency. Butsince the electric power required is usuallygenerated in a separate, immobile plant, there issome power loss in the line transmission, and thecatenary system represents a considerable invest-ment and maintenance expense. Electric locomo-tives, in general, are economical only on lineshaving fast and frequent train schedules. Theselocomotives have the advantages of being able todevelop a high horsepower at high speed andrequiring less maintenance than diesel-electric.
19.19 Propulsion PowerRequirements forTrains
These vary with the type of service. For intercitypassenger and freight trains, the power to pull thetrains up grades and make the scheduled time is ofparamount importance. For commuter and rapid-transit service, an important factor in the powerrequirement is the need to accelerate quickly. Forpersonal rapid transit, the speed is relatively slow,but power must be adequate to accelerate quicklyto the desired speed. For all types of service, powermust be adequate to overcome grade, curve, androlling resistance. Requirements for running time,frequency of service, and operating costs must allbe considered.
19.19.1 Resistances to TrainMovement
Grade resistance, offered by an ascending grade,equals 20 times the percent grade per ton of train.Thus, on a 1.5% grade, the grade resistance is 30 lb/ton; on a 1.0% grade, 20 lb/ton; and on a 0.5%grade, 10 lb/ton. On a descending grade, the sameforces accelerate the train, which must be con-trolled by braking.
Curve resistance is the added resistance re-quired to guide and slip the wheels in negotiating acurve. Curve resistance is generally consideredequivalent to 0.04% grade per degree of curvature.
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
Thus, the curve resistance on a 48 curve would be0.04 � 20 � 4 ¼ 3.2 lb/ton of train. It is customaryon ruling grades to compensate for curvature byreducing the grade for the length of the curve.Thus, if the ruling grade on a line is 0.5%, com-pensated for curvature, no consideration need begiven to curve resistance in calculating powerrequirements because it is already included in thegrade. Use of rail lubricators reduces curve resis-tance by about one-half. Curve resistance tends toretard the train on descending grades.
Rolling or train resistance is the resistance totrain movement on level tangent track. Trainresistance is affected by speed, weight on the axle,and characteristics of the track. This last factor isusually neglected because it is relatively small.Starting resistance is less with roller bearings, butafter a train starts, the train resistance is about thesame for roller and solid bearings. For example, thestarting resistance for a car with solid bearingsmight be as much as 20 lb/ton, but train resistancebecomes 5 lb/ton as soon as the car is in motion.The same car on roller bearings would have thesame starting resistance as when moving at slowspeed, 5 lb/ton.
19.19.2 Formulas for TrainResistance
There are several formulas for calculating trainresistance. The Davis formulas (W. J. Davis, Jr.,“The Tractive Resistance of Electric Locomotivesand Cars,”General Electric Review, October 1926) arerepresentative of results found by several investi-gators. According to the AREA “Manual forRailway Engineering,” the Davis formulas havegiven satisfactory results for speeds between 5 and40 mi/h. However, the increased dimensions andheavier loading of freight cars, the much higheroperating speed of freight trains, and changes intypes of cars since the formulas were developedhave made it desirable to modify the constants inthe Davis equation. Recent tests have shownimproved results with the following modifiedDavis formula:
R ¼ 0:6þ 20
Wþ 0:01V þ KV2
WN(19:19)
where R ¼ resistance, lb/ton
W ¼ weight per axle, tons
N ¼ number of axles per car
V ¼ speed, mi/h
K ¼ air resistance coefficient
¼ 0.07 for conventional freight-trainequipment
¼ 0.16 for trailer on flatcar (piggyback)
¼ 0.0935 for containers on flatcars
The last term in this equation, KV2/WN,represents the air drag due to train speed. At highspeeds, this becomes a major factor in trainresistance, and it is necessary to take into accountthe cross-sectional area of the car, aerodynamicproperties of the car design, air density, and windvelocity and direction.
For a detailed treatment of this subject for high-speed passenger service, see J. L. Koffman,“Tractive Resistance of Multi-Unit and Locomo-tive-Hauled Passenger Trains,” Rail EngineeringInternational, April-May 1973. The author suggeststhe following formula as representative of modernpassenger-train equipment on British and Con-tinental railways:
R ¼ 1:5W þ (5:5þ n� 2)V
10
� �2
(19:20)
where R ¼ total tractive resistance of conventionalpassenger train, kg
W ¼ total weight of train, metric tons
n ¼ number of coaches in train
V ¼ train speed, km/h
and the effective locomotive and coach frontal areais taken to be 10 m2. Equation (19.20) assumes anair drag coefficient of 0.6 based on experimentaldata on a locomotive at speeds up to 100 mi/h.With some car designs where little considerationwas given to aerodynamic properties, the air-dragcoefficient was found to be as much as 1.85 for aneight-car train. On the other hand, it was found tobe as little as 0.97 for a 249.5-m-long, 10-coachTokaido train, for which extensive model tests weremade in a wind tunnel to obtain good aerodynamicperformance. The Association of American Rail-roads continues to test new equipment and updatevalues.
In design of vehicles to be operated at speedsover 100 mi/h, it is highly important that aero-dynamic performance be considered because airdrag causes most of the rolling resistance at these
Running time and fuel consumption are usefuldata in comparing the relative desirability ofvarious lines in new construction or in revisionsof existing lines. Running time may be calculatedby the velocity-profile method.
In this method, accelerating force, lb/ton, iscomputed by subtracting from the drawbar-pullcharacteristics of the locomotive the train resistanceon level track. The computation is repeated for5-mi/h increments from starting to maximumpermitted operating speed. Since grade resistanceis 20 lb/ton (see Art. 19.19.1), the accelerating forcemay be converted into an equivalent grade bydividing by 20. The actual profile of the line isplotted on a graph showing elevations versusdistance. On the same graph, for each increment ofspeed, the equivalent grade is plotted betweenpoints for which the vertical difference between theactual and equivalent grades equals the velocityhead. The velocity head, ft, for any speed is
VH ¼ 0:035V2 (19:21)
whereV ¼ speed, mi/h. This formula expresses thekinetic energy of a train due to its velocity and therotating energy in its wheels as equivalent potentialenergy due to height. The same procedure isapplied for braking to reduce speed or stop. Theseries of lines representing equivalent grades is thevelocity profile. (Detailed instructions for trainperformance calculations are in “Manual forRailway Engineering,” American Railway Engi-neering and Maintenance of Way Association.)After the velocity profile has been completed forthe line, the running time is found by summing thetime required to travel each increment of distanceat the average speed for the increment. A computermay be used to facilitate and expedite the calcu-lations required.
The time that a locomotive will be working atfull capacity, part capacity, or drifting can bedetermined from the velocity profile. Multiplyingeach period of time by the corresponding rate atwhich fuel is used by a particular locomotive yieldsthe fuel consumption. Another method that maybe used to calculate fuel consumption is to first
figure the total work done. This consists of thework done in overcoming rolling resistance, plusthe resistance of gravity on ascending grades, plusthe resistance due to curvature. From this sumshould be subtracted the energy of gravity ondescending grades, but the loss of energy (velocityhead) due to application of brakes should be addedto give total work.
The total work done, ft-lb, may be converted togallons of diesel fuel bymultiplying by 4 (efficiencyof 25%) and dividing by 90 million (ft-lb of energyper gallon of diesel fuel).
A simpler method that will be sufficientlyaccurate for most purposes is as follows: Approxi-mate a condensed profile of the line with a series oflong grades. Calculate the speed at which thelocomotive can handle the train over each grade.Obtain the time over each grade by dividing thedistance by the speed and total these. Add anarbitrary 5 to 10 min for each stop and start,depending on the length of the train. This will givethe approximate running time. The fuel consump-tion can be determined as in the velocity-profilemethod or from total work done.
19.19.4 Train Tonnage
The maximum tonnage that can be hauled over aline with a given locomotive is determined by theruling gradient. However, the locomotive may notbe able to handle this much tonnage at a highenough sustained speed to meet competitive trafficrequirements or to avoid train-crew overtime. Withdiesel-electric locomotives, any number of unitscan be coupled together, but if the locomotives areplaced at the head end of the train, trouble withbroken couplers may be encountered if drawbarpull exceeds 200,000 lb.
If a train is made very long, for example, 200cars, difficulty may be experienced from slackrun-in, from excessive delays for replacement ofbroken couplers or setting out cars that havedeveloped hot boxes, or from air-brake operationin very cold weather. A train of 100 cars is quitecommon in the United States. Occasionally, rail-roads operate trains with as many as 250 cars.Diesel-electric locomotives are sometimes addednear midlength of a train and as pushers at theend on steep grades.
Generally, the more tonnage in a train, the lowerthe operating cost. Thus, train tonnage is a matterof economy, practicality of operation, and meeting
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
competitive traffic requirements for speed andfrequency of service.
Since train resistance varies with car weight andnumber of cars, a locomotive cannot handle asmuch tonnage in a train of empty cars as in one ofloaded cars. Also, a locomotive cannot handle asmuch tonnage in cold weather as in warm weather.As a convenient means of compensating for thesetwo factors, use may be made of the data inTable 19.8.
The adjusted tonnage rating may be consideredas the sum of the weight of cars and contents, tons,and an adjustment, tons. For temperatures above35 8F, this sum is called the adjusted tonnage Arating. The adjustment for computing the adjustedtonnage A rating is obtained by multiplying theadjustment factor given in Table 19.8 for a specificruling grade by the number of cars in a train. Fortemperatures below 35 8F, a percentage of the Arating is used, as indicated in Table 19.8. Theadjusted tonnage rating is independent of thenumber of cars in a train.
19.20 Train Control and SignalSystems
There are many methods for controlling the move-ment of trains on tracks, depending on the numberof tracks and the characteristics of the traffic. Theobjective is to move the trains to conform to desired
schedules between departure and destinationpoints, with safety the paramount consideration.
Train orders and time schedules are usedwhere only a few trains move over a line per day.Passenger train speeds are limited to 59 mi/h andfreight train speeds to 49 mi/h by the FederalRailroad Administration (FRA) where this methodof train control is used.
The manual-block system provides a saferoperation. Operators stationed between blocks oftrack do not permit a train to enter the next blockuntil notifiedby the operator at the other endof blockthat it is clear. Although safe, this method gives lowtrack capacity, slow schedules, and high cost forblock operators. With the manual-block system,speeds up to 79 mi/h are permitted by FRA order.
The automatic-block signal system providesfor successive blocks of tracks to be separatedelectrically by insulated rail joints at both ends.Unless the rail is continuously welded, rail bondsare used at each bolted rail joint to ensurecontinuity of the electric circuit between rail ends.A three-position signal aspect is connected into theelectric circuit for each block and for adjoiningblocks. Many different types of signal aspects areused. A common signal aspect is a green light toshow an approaching train that two blocks aheadare clear, a yellow light to show that the secondblock ahead is occupied, and a red light to showthat the next block ahead is occupied. The blocklength should not be less than the service braking
Table 19.8 Data for Calculating Adjusted Tonnage Ratings
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
distance required for the train speed. A blocklength of 1 mi is frequently used. Speeds up to79 mi/h are permissible.
Automatic train control is provided by awayside inductor located in advance of each blockcircuit over which the locomotive receiver passes.This receiver is mounted on the locomotive journalbox to have 11⁄2-in clearance with the waysideinductor. An electric circuit is provided so thatwhen a locomotive passes a restrictive signal, theengineman must acknowledge awareness byactuating a contactor; otherwise, the train brakesare automatically applied. With this system, trainspeed is not limited by FRA order to 79 mi/h.
Coded control has the advantage of using onepair of line wires to transmit the signals fromblocks ahead instead of requiring many line wiresfor this purpose. An interruption of the dc voltageis used for different signal indications. Forexample, on track with one-direction movement,180 interruptions per minute operates the “pro-ceed” signal; 120, the “approach-medium”; 75, the“approach”; and no code, the “restrictive.”Additional signals may be transmitted by combi-nations of reversed polarity.
Another advantage of coded control is that thecode-following track relay must pick up with eachpulse. Therefore, the train shunt need only beenough to reduce the track current at the relaybelow the pickup value, rather than below thedropout value. This permits higher track voltage tobe used, and for given ballast resistance conditions,track circuits can be made twice as long.
Continuous cab signals are provided by usingalternating current for the track circuits instead ofdirect current and placing inductive receivers infront of the leading wheels on the locomotive.Thus, the signal passing through the rails istransmitted by the receivers to give signals in thelocomotive cab. Any change in signal aspect isimmediately visible, whether or not the waysidesignal is in sight of the engineman. With thissystem, wayside signals are not actually required.Coded control can be used with this system byinterrupting the ac voltage in the same manner asfor dc voltage. With continuous cab signals, trainspeed may exceed 79 mi/h.
Interlocking is usually provided at railroadgrade crossings and at some turnouts. At crossingswithout interlocking, each train must first stopat the crossing and then proceed if the crossingis clear.
Mechanical interlocking operated by a tower-man permits giving the right-of-way to one train,holding any on the track being crossed. Signalaspects are operated by levers and long pipeconnectors, as are derails on each track.
Electric interlocking permits the operator toactuate signal aspects and derails electrically. Theoperator can also unlock and throw switches byelectric control for crossovers or connecting tracks.Switches are thrown by electropneumatic orelectric motor switch machines. Safety features areprovided to prevent an operator from lining upsignals, derails, and switches unless the track isclear for such movements.
For very complicated crossings involving manytracks and train movements, route interlocking isused. It is necessary for the operator to just push abutton for the point where a train will enter theinterlocking and another button for the pointwhere the train is to leave. The best available routewill then be automatically selected and lined up forthe train. On simple crossings, train movementsthrough an interlocking can be controlled auto-matically by an electric signal system.
Overlap and absolute permissive blocksignaling is required to avoid collision of trainsmoving in opposing directions on the same track.With automatic-block signals giving indicationsfor only two blocks ahead, opposing trains couldpass a clear signal simultaneously and find thenext signal at stop but be unable to do so in time.This situation can be prevented by overlappingthe advance blocks so that the stop aspect isdisplayed more than one block in advance of atrain. With the absolute permissive block system,relays can be used to extend the blocks in advancebut provide the normal block indications forfollowing trains, thus expediting their movement.Where opposing trains are operated on the sametrack with absolute permissive block, the blockcontrol is extended far enough in advance toinclude a passing track or crossover so that thetrains can pass.
Centralized traffic control (CTC) is officiallydesignated by the FRA as the “traffic-controlsystem.” It is defined as “a block system underwhich train movements are authorized by blocksignals whose indications supersede the super-iority of trains for both opposing and followingmovements on the same track.”
With CTC, one operator directs the movementof all trains and usually of all switches and derails
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
on the trackage under his or her control. For low-traffic-density lines, sometimes the switches aremanually thrown by the trainman in accordancewith a signal aspect at the switch. A panelboardshows the operator a diagrammatic layout of thetrackage, with all turnouts identified and signalaspects at turnouts shown. Lights identify the loca-tion of all trains. Signals and switches at the ends ofpassing tracks are arranged as route-type inter-locking. Automatic-block signaling controls move-ment between passing tracks. With only two linewires along the track and different frequencies fortransmitting coded data, it is possible for oneoperator to control train movement over severalhundred miles of trackage. The actual operation isperformed on a small control board in front of theoperator, who merely pushes buttons or turnssmall switches to send out the directing signal.Acknowledgment is indicated on the panelboardby a signal automatically sent back when the actionhas been completed.
Automatic train operation is the capability forcomplete scheduling and operation of trains,including starting and stopping, opening andclosing doors, and so on, by computer command.Theoretically, a train attendant is not required.Actually, it is usually considered desirable ifpassenger traffic is involved to have an attendanton each train who can take over in an emergencyand override the automatic operation with manualoperation. For manual override, automatic-blocksignals or continuous cab signals are required.Also, presence of a train attendant may give thepassengers a sense of security.
At the control center, one or more computerscontrol the operation of each train according toschedule but have the capability to change theoperation automatically as required by any delaysthat may occur. One or more “dispatchers” areprovided to observe the control board showing theposition of all trains and to take over manualoperation in an emergency. Experience has shownthat automatic train operation will get trains over aroute in less time and with more comfort to passen-gers than can be obtained with manual operation.
The systems and procedures for train control tosecure maximum performance have become sosophisticated that specialists in the field should beconsulted for selection and design of a system forany given conditions.
Grade-crossing warning is an important signalfunction in train operation. Block-signal track
circuits may be used to actuate flasher lights orcrossing gates automatically to warn vehicles ofapproaching trains at highway grade crossings.Crossing gates are advantageous at crossings oftwo or more tracks because of the danger that amotorist will drive on the crossing after a train hascleared without waiting to see if a train may beapproaching on another track.
Audiofrequency overlay circuits have beendeveloped to actuate grade-crossing protectionwithout the need for insulated rail joints.
Slide fences are frequently used at locationswhere falling rocks obstruct the track. Thesefences are drawn tight by spring tension at oneend. The pressure of a rock at any point on thefence will cause end movement, which breaks anelectric circuit, causes a control relay to becomedeenergized, and sets the block signal to a stopposition.
Additional types of wayside detectors includethose to find broken wheels, high-wide loads,dragging equipment and overheated bearings(“hot box”). High-wide load detectors use wiresor radar type units to pick up any shifted or extradimensional loads that may exceed the allowableclearance of a tunnel or through truss bridge.Dragging equipment detectors use boards placedboth outside and inside the rails that rely onphysical contact with anything that may behanging below the normal equipment clearances.Hot box detectors use heat sensitive equipment tocompare the heat of passing cars and locomotives’bearings to predetermined limits. Many of thesedetectors are now equipped with radio warningmessages that are transmitted to the dispatcher andthe train engineer.
19.21 Communication inTrain Operation
Many types of communication are available toenhance the safety and performance of train oper-ation and give passengers a feeling of security.These include simple communication by means ofa train whistle or warning bell, wayside or cabsignals, telephone, radio, microwave, and elec-tronic direct circuit or inductance. Many of thesehave been discussed in Arts. 19.17, and 19.20.Specialists in the communications field should beconsulted on selection and design of the most
Any use is subject to the Terms of Use as given at the website.
RAIL-TRANSPORTATION ENGINEERING*
suitable communication system for a given railwayoperation.
In the late 1960s, some railroads tried anautomatic car-identification system in which barcodes were placed on the sides of cars and read byoptical scanners. Because of difficulties in keepingthe codes clean, the scanners were not alwayssuccessful in reading the codes, and the systemwas abandoned. The railroads also tried various
systems in which personnel located in yard facil-ities used television cameras to verify car numbersas the cars entered or exited major yards. Onecurrent form of car identification consists of shortrange transponders to pick up signals from tagsattached to the cars. In addition, satellite systemsutilizing the global positioning system (GPS)are under development to monitor train move-ments.
