SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Rail Capacity Workshop Capacity Constraints and Remedies
Curves Grades Station stops Bridges Diamonds Track maintenance and renewal
22 September 2010
Curves
Curve Components
TC CT
PI
M
E
100 ft
D
X
Y
Curve whose degree changes uniformly with distance from origin
Used to: transition from tangent alignment to
curve or between consecutive curves introduce curve superelevation
Circular Curve
Spiral
Curve of constant degree (radius) Used to change alignment direction May connect to tangents or other
curves Introduced by spirals in higher-
speed track
Mild curvature: D ≤ 2º
Medium Curvature: 2º < D ≤ 8º
Sharp Curvature: 8º < D ≤ 12º
Extreme Curvature: D ≥ 12º
Impacts of Curvature Restricted train speed Increased train resistance
0.08 lb per train ton per curve degree Affects acceleration time, power requirements
Increased maintenance Track alignment and elevation Rail and wheel wear
Greater potential for derailment
Curve Forces
W W W
R R R
F F F
Direction of curve
Relative forces on rails
(a) Speed < Balanced Speed (b) Speed = Balanced Speed (c) Speed > Balanced Speed
Curve Speed Limit
Vmax = maximum allowable train speed, mph Ea = outside rail elevation, inches Eu = allowable cant deficiency, inches
3 inches for conventional equipment 4 inches for certified equipment higher where approved by FRA
D = degree of curve
DEEV ua
0007.0max
Train Speeds Through Curves (Unconstrained)
0
20
40
60
80
100
120
140
160
1 2 3 4 5 6 7 8 9 10
Degree of Curvature
Max
imum
Tra
ck S
peed
(mph
)
4½” superelevation
Inte
rmod
alFr
eigh
tPa
ssen
ger (
conv
entio
nal e
qpt.)
Pass
enge
r (tilt
eqp
t.)
Mitigating Delay due to Curves Increase curve elevation
FRA maximum for track classes 3-5 is 7 inches Generally requires spiral length adjustment Consider effect on clearances, structures, crossings
Provide proper spiral design Rate of elevation change limits speed
Qualify equipment for greater cant deficiency Realign track
Reduce curve degree Reduce number of curves
Extend sidings to reduce length of single track Reduces meet delay in speed limited territory
Vertical Alignment Consists of grade tangents connected by
parabolic vertical curves Grade tangent has uniform change in elevation
over distance (expressed as percent) Smooth transition between grade tangents
provided within length of vertical curve
G1 G2
PVC PVT
L
L/2 L/2
x
y
PVI
Impacts of Grades Grade force is 20 lb per train ton per
percent Grades can severely affect:
Maximum sustained train speed (upgrade) Acceleration (upgrade) Train speed control (downgrade) Stopping distance Train buff and draft forces
Curves add resistance and limit speeds, further increasing impact of gradesImpact potential of sustained grades:
Low G ≤ 0.25%Moderate 0.25% < G ≤ 0.75%High 0.75% < G ≤ 1.5%Very High G> 1.5%
Types of Grades Ruling grade: train with minimum P/W
ratio can crest at crawl speed within motive power short-time limits
Momentum grade: train with minimum P/W ratio will crest with some speed reduction from track speed
Helper grade: train gets temporary additional power added to help crest grade
Riprap territory: undulating profile requires care to control buff/draft forces in long trains
Reducing Grade Impacts Raise P/W ratio on freight trains
May increase speeds on ascending grades Reduce need for capacity consuming helper and
doubling operations Increase power and tonnage on freight trains
Longer trains can reduce train volume, free up slots Especially useful with distributed power
Avoid stopping train on severe upgrades Provide operating authority to pass restricting
signals at low speed Provide power switches at sidings
Engineering Approaches to Grade Management
Change alignment to reduce grade Typically involves major capital investment May increase track length, curvature Potential complications, delays from R-O-W
acquisition, permitting Tunneling, large cuts can introduce additional
maintenance issues Requires careful assessment of economics
Lengthening vertical curves Improves train handling Increases ride comfort at speed
Engineering Approaches to Grade Management
Provide multiple main tracks on long grades to permit passes and overtakes of slow trains
Provide auxiliary tracks at top and bottom of grade to: Clear helper movements Reduce delay by trains requiring setup/release of
retainers Prevent blockages while doubling
Electrification Allows increase in train power, regenerative braking Major capital investment, economics sensitive to fuel
prices
Impacts of Station Stops Each stop requires time for deceleration,
station dwell, and acceleration Average train speed decreases as number and
spacing of stations increases Close spacing may not permit train to accelerate to
track speed between stations Inefficient platform configuration may increase dwell
Stopping trains may delay other traffic Through trains may have to slow at stations to
reduce risk to passengers
SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Mitigating Factors for Station Stops
Provide train P/W ratio to achieve performance goals considering desired dwell time and station spacing
Provide for meets and passes at stations where warranted by traffic demands Sidings Multiple main track
Optimize platform configuration to minimize dwell time Adequate length to match access points with
demand High-level fastest loading/unloading
22 September 2010
SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Operational Impacts of Bridges Reduced train speed due to bridge design
or condition Restrictions on traction/braking due to
bridge design or condition Equipment restrictions due to bridge
design or construction Restricted train speed approaching
movable bridge Delays imposed by open movable bridges
22 September 2010
Reasons to Speed Restrict Bridge
Bridge condition or structural design inadequate to withstand Speed related impact loads Speed related lateral loads
Reduce load effects on critical structures Remediate track condition defects Permit train crew verification of movable
bridge position Reduce derailment risk at movable span
Movable Bridges
Types Lift bridge Bascule (draw) bridge Swing bridge
Open/close cycle time influences delay
Can be significant capacity constraint with heavy water traffic
More to go wrong than conventional designs
Track Crossings Track capacity
reduced by crossing movements
Approaching train must be protected against conflicting movement May limit speed,
increase occupancy time
High maintenance location due to impact loading Problems increase
with speed
Flangeway
Crossing Improvements Reduce maintenance requirements
Provide premium components Replace with One-Way Low Speed (OWLS) design
Replace with turnouts Improves reliability, operational flexibility Realignment of track costly, particularly for right-angle
crossings Crossing movements still consume capacity
Provide interlocking with distant signals to reduce approach delay Automatic-first come, first served Dispatcher/operator controlled-can prioritize traffic
Grade separate Costly, uses more real estate Permanently solves capacity issues
SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Track Maintenance Railroads must inspect and maintain
track Track must comply with federal Track
Safety Standards (49 CFR Part 213) Track maintenance workers and
machinery must be protected from train traffic in accordance with 49 CFR Part 214
The impact of these requirements on track capacity must be considered
22 September 2010
Maintenance Activities Inspect track Service and adjust special trackwork and track appliances Replace or repair worn track components Replace failed track components Keep track in proper gage, alignment, and surface Maintain stormwater drainage elements Correct ballast drainage problems Address subgrade problems Control vegetation Manage thermal loads in CWR track Distribute materials for projects Repair storm or derailment damaged track Reconstruct track to higher standards
Factors Influencing Track Maintenance Needs
Characteristics of track system Rail and rail fasteners Crossties Ballast
Track horizontal and vertical alignment Effectiveness of track drainage Nature of track subgrade Traffic volume and mix Maximum train speed Maximum wheel loading Climate
Speed and Track Condition Owner sets train speed limits (pax, freight) Speeds establish federal track class Track condition must meet requirements
for class If track condition does not meet
requirements, owner must take immediate remedial action Repair Reduce track class to make defect compliant Remove track from service
SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Track Classes
22 September 2010
Track ClassMax. Freight Speed (mph)
Max. Passenger
Speed (mph)1 10 152 25 303 40 604 60 805 80 906 110 1107 125 1258 160 1609 200 200
Categories of Defects Class specific
Defect may become compliant by reducing track class (slow ordering)
Examples: gage, alignment, mismatch Non-class specific
Defect is non-compliant regardless of track class
Examples: drainage, vegetation Speed defined
Defect type requires specific limiting speed Example: rail defect, minimum curve elevation
Track Maintenance Approaches Working under traffic conditions
Practical for many types of work Trains may pass through work site while work is
in progress Typically requires speed reduction Need to clear on-track equipment adds delay Workers must have protection per Part 214
Taking track out of service Necessary for some times of work May simplify Part 214 compliance Capacity unavailable until work complete
SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Mitigating Capacity Impacts Limit duration of slow orders for defect remediation
on main tracks Address root causes of maintenance problems Minimize on-track time for forces
Employ hi-rail equipment where practical Provide nearby clearance location for on-track equipment Prefabricate track panels and pre-position materials Use high-production equipment and techniques
Schedule work during off-peak periods Have close liaison between operations and engineering Consider need to provide for night work, lower
productivity
22 September 2010
SCORT/TRB Rail Capacity Workshop - Jacksonville Florida
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Mitigating Maintenance Impacts Consider life-cycle costs of track components
Premium components can reduce maintenance needs Include operating cost impacts of maintenance
Employ “blitz” approach Plan all possible work in zone, perform during
shutdown Design to reduce impacts of maintenance on
operations Increase spacing between main tracks and sidings Provide crossovers in multiple track territory Consider maintenance in design of yards and
terminals
22 September 2010