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ECGD 4121 – Transportation Engineering IECGD 4121 – Transportation Engineering I

Lecture 4Lecture 4

Faculty of Applied Engineering and Urban PlanningFaculty of Applied Engineering and Urban Planning

Civil Engineering DepartmentCivil Engineering Department

22ndnd Semester 2008/2009 Semester 2008/2009

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Traffic EngineeringTraffic Engineering

CharacteristicsCharacteristicsofof

System ComponentsSystem Components

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Components of Highway ModeComponents of Highway Mode

System Components:System Components:

• DriverDriver

• Pedestrian (and others)Pedestrian (and others)

• Vehicle:Vehicle:

Passenger vehiclePassenger vehicle

Heavy truckHeavy truck

BusBus

• Road pavementRoad pavement

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Impact of Interaction amongImpact of Interaction amongDriver – Vehicle - RoadDriver – Vehicle - Road

Impact the following design parameters:Impact the following design parameters:• Length of acceleration and deceleration Length of acceleration and deceleration

laneslanes• Maximum highway gradesMaximum highway grades• Minimum turning radiusMinimum turning radius• Lane widths and clearance heightsLane widths and clearance heights• Location of traffic controlsLocation of traffic controls• Speed limits and traffic signal timingSpeed limits and traffic signal timing• Stopping sight distancesStopping sight distances• Sight passing distancesSight passing distances• Roadside safety featuresRoadside safety features

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System CharacteristicsSystem Characteristics

• Human CharacteristicsHuman Characteristics

Visual ReceptionVisual Reception

Hearing PerceptionHearing Perception

Perception-Reaction ProcessPerception-Reaction Process

• Vehicle CharacteristicsVehicle Characteristics

Static and Dynamic CharacteristicsStatic and Dynamic Characteristics

• Road CharacteristicsRoad Characteristics

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• Human as an active essential component of Human as an active essential component of traffic system, distinguishes TE from virtually all traffic system, distinguishes TE from virtually all other CE fields.other CE fields.

• This component is widely variable and may be This component is widely variable and may be unpredictable in capabilities and characteristics.unpredictable in capabilities and characteristics.

• PhysiologicalPhysiological

Measurable and usually quantifiableMeasurable and usually quantifiable

• PsychologicalPsychological

More difficult to measure and quantifyMore difficult to measure and quantify

Human CharacteristicsHuman Characteristics

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Human CharacteristicsHuman Characteristics

• Perception-Reaction Time (PRT)Perception-Reaction Time (PRT)

• Visual ReceptionVisual Reception

• Walking SpeedWalking Speed

• Hearing PerceptionHearing Perception

• Actions taken by drivers depend on their Actions taken by drivers depend on their

ability to receive, evaluate, and respond to ability to receive, evaluate, and respond to

expected and unexpected situationsexpected and unexpected situations

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Driver:Driver:

• Wide range of system usersWide range of system users

• Wide range of drivers use the system:Wide range of drivers use the system:

Ages: from 16 up to 80 years oldAges: from 16 up to 80 years old

Various mental and ethical conditionsVarious mental and ethical conditions

Physical abilities (sight, hearing, etc)Physical abilities (sight, hearing, etc)

ExperienceExperience

Human CharacteristicsHuman Characteristics

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• Driving is the task of monitoring and Driving is the task of monitoring and responding to a continuous series of responding to a continuous series of visual and audio cuesvisual and audio cues

• Driving task has three levels:Driving task has three levels: Operational (Control): vehicle control Operational (Control): vehicle control

through second-to-second driver’s through second-to-second driver’s actions, speedactions, speed

Tactical (Guidance): vehicle guidance Tactical (Guidance): vehicle guidance through maintenance of a safe speed through maintenance of a safe speed and proper pathand proper path

Strategic (Navigation): route planningStrategic (Navigation): route planning

Human CharacteristicsHuman Characteristics

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Driver decision process involves:Driver decision process involves:

• SensingSensing

• PerceivingPerceiving

• AnalyzingAnalyzing

• DecidingDeciding

• RespondingResponding

Human CharacteristicsHuman Characteristics

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SensingSensing• Feeling: forces on the vehicleFeeling: forces on the vehicle• Seeing: critically important means of Seeing: critically important means of

acquiring information:acquiring information: Ability to see fine details, depth Ability to see fine details, depth

perception, peripheral vision, ‘night’ perception, peripheral vision, ‘night’ vision, glare recoveryvision, glare recovery

• Hearing: important for drivers, cyclists and Hearing: important for drivers, cyclists and pedestrianspedestrians

• Smelling: detecting emergencies e.g. Smelling: detecting emergencies e.g. overheated engine, burning brakes, fireoverheated engine, burning brakes, fire

Human CharacteristicsHuman Characteristics

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• Perception time is delay between visibility and Perception time is delay between visibility and determining there is a potential hazarddetermining there is a potential hazard

• Perception and Reaction time consists of four Perception and Reaction time consists of four stagesstages Perception: Sees or hears situationPerception: Sees or hears situation Identification: Identify situationIdentification: Identify situation Emotion: Decides on course of action Emotion: Decides on course of action

(swerve, stop, change lanes, etc.)(swerve, stop, change lanes, etc.) Reaction: Acts (time to start events in Reaction: Acts (time to start events in

motion but not actually do action). Foot motion but not actually do action). Foot begins to hit brake, not actual deceleration.begins to hit brake, not actual deceleration.

Human CharacteristicsHuman Characteristics

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• Perception-reaction time usually ranges Perception-reaction time usually ranges

between 0.5 to 7.0 seconds.between 0.5 to 7.0 seconds.

• Perception-reaction time is often assumed to Perception-reaction time is often assumed to

be 2.5 seconds (true for about 85% of drivers).be 2.5 seconds (true for about 85% of drivers).

• At 100 km/hr a vehicle travels about 70 meters At 100 km/hr a vehicle travels about 70 meters

during that time interval.during that time interval.

Human CharacteristicsHuman Characteristics

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Perception-Reaction Time FactorsPerception-Reaction Time Factors

• Environment:Environment: Urban vs. RuralUrban vs. Rural Night vs. DayNight vs. Day Wet vs. DryWet vs. Dry

• AgeAge• Physical Condition:Physical Condition:

FatigueFatigue MedicalMedical Drugs/AlcoholDrugs/Alcohol

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• Visual acuity and ability (Visual acuity and ability (lighting conditions, lighting conditions,

presence of fog, snow, etc.presence of fog, snow, etc.))

• Complexity of situation and complexity of Complexity of situation and complexity of

necessary response (necessary response (more complex more complex more more

time is consumedtime is consumed))

• Expected versus unexpected situation (Expected versus unexpected situation (traffic traffic

light turning red vs. dog darting into roadlight turning red vs. dog darting into road))

Perception-Reaction Time FactorsPerception-Reaction Time Factors

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Effect of Task ComplexityEffect of Task Complexity

wherewherettrr = = reaction time (s)reaction time (s)aa = = minimum reaction time under different minimum reaction time under different

alternative circumstances (s)alternative circumstances (s)bb = = 0.13 (slope)0.13 (slope)NN = = no. of alternativesno. of alternatives

Nbatr 2log

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Visual AcuityVisual Acuity

• Visual acuity: Visual acuity: It refers to the sharpness with It refers to the sharpness with

which a person can see an object.which a person can see an object.

• One measurement of it is the recognition One measurement of it is the recognition

acuity obtained using Snellen Chart.acuity obtained using Snellen Chart.

• Visual acuity is either static when no motion Visual acuity is either static when no motion

is involved, and dynamic when relative motion is involved, and dynamic when relative motion

is involved.is involved.

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Snellen ChartSnellen Chart

• A person with normal A person with normal visual acuity (20/20) visual acuity (20/20) can recognize 1/3” can recognize 1/3” letters under well letters under well lighting conditions lighting conditions from 20’from 20’

• A person with 20/40 A person with 20/40 requires object be requires object be twice as large at twice as large at same distancesame distance

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ExampleExample

• A driver with 20/20 vision can see signs up to A driver with 20/20 vision can see signs up to 90’ away. How close must a driver with 20/50 90’ away. How close must a driver with 20/50 vision be?vision be?

• X = (90)[(Bad/Good)] = (90)[(20/50)/(20/20)]X = (90)[(Bad/Good)] = (90)[(20/50)/(20/20)]• X = 36’X = 36’• If those letters were 2” high, how high should If those letters were 2” high, how high should

they be for a driver with 20/60 visions (same they be for a driver with 20/60 visions (same distance)?distance)?

• H = (2)(Good/Bad) = (2)[(20/20)/(20/60)]H = (2)(Good/Bad) = (2)[(20/20)/(20/60)]• H = H = 6 6 ’’

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Static Acuity and Letter SizeStatic Acuity and Letter Size

Acuity (ft/ft)Acuity (ft/ft) 20/1020/10 20/2020/20 20/3020/30 20/4020/40 20/5020/50 20/6020/60

Index L/H (ft/in)Index L/H (ft/in) 114.6 114.6 57.3 57.3 38.2 38.2 28.7 28.7 22.9 22.9 19.1 19.1

• Visual acuity is worse when an object is movingVisual acuity is worse when an object is moving

• During night conditions, the visual acuity is one During night conditions, the visual acuity is one column worsecolumn worse

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ExampleExample

How large should the letters size be to be recognizable How large should the letters size be to be recognizable at a distance of 90 ft by a person with the 20/60 vision?at a distance of 90 ft by a person with the 20/60 vision?

)50/20(20/2050/20 LL

ft36)50/20(9050/20 L

ft/in1.19)/( 60/20 HL

nchH i7.41.19/9060/20

A driver with 20/20 vision can read a sign from A driver with 20/20 vision can read a sign from a distance of 90 ft. How close must a person a distance of 90 ft. How close must a person with the 20/50 vision be in order to read the with the 20/50 vision be in order to read the same sign?same sign?

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Roadway Sign ReadabilityRoadway Sign Readability

• Maximum distance a driver can read a road Maximum distance a driver can read a road sign within his vision acuity =sign within his vision acuity =

(letter height in inches)*(vision acuity)(letter height in inches)*(vision acuity)• Example:Example:

letter height of road sign = 4 inchesletter height of road sign = 4 inches a driver can read a road sign at a distance a driver can read a road sign at a distance

of 28.7 ft for each inch of letter heightof 28.7 ft for each inch of letter height• Solution:Solution:

readability = (4 in)(28.7 ft/in) = 114.8 ftreadability = (4 in)(28.7 ft/in) = 114.8 ft

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Sign LegibilitySign Legibility

A sign should be legible at a sufficient distance A sign should be legible at a sufficient distance in advance so that the motorist gets time to in advance so that the motorist gets time to perceive the sign, its information, and perform perceive the sign, its information, and perform any required maneuver.any required maneuver.

Rule of thumb:Rule of thumb:LD = 50HLD = 50H

where:where:LD = Legibility distance (ft), andLD = Legibility distance (ft), and

H = Height of letters on the sign (inch)H = Height of letters on the sign (inch)

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Human Visual FactorsHuman Visual Factors

Visual Acuity Factors:Visual Acuity Factors:• 20° cone of satisfactory vision 20° cone of satisfactory vision • 10° cone of clear vision (traffic signs and 10° cone of clear vision (traffic signs and signals should be within this cone)signals should be within this cone)

• 3° cone of optimum vision3° cone of optimum vision• 160160° cone of vision defines the peripheral vision ° cone of vision defines the peripheral vision (Driver can see object but with no clear details)(Driver can see object but with no clear details)

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Aging Impact on VisionAging Impact on Vision

• Older persons experience low light level:Older persons experience low light level: Rules of thumb – after 50 the light you can Rules of thumb – after 50 the light you can

see halves with each 10 yearssee halves with each 10 years

• Glare – overloading eye with light:Glare – overloading eye with light: Older drivers can take twice as long to Older drivers can take twice as long to

recover from glarerecover from glare

• Poor discrimination of colorPoor discrimination of color

• Poor contrast sensitivityPoor contrast sensitivity

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Pedestrian CharacteristicsPedestrian Characteristics

Walking Speed:Walking Speed:

• 4.0 fps Safe or 154.0 fps Safe or 15thth

• 5.0 fps Median or 505.0 fps Median or 50thth

• 6.0 fps or 856.0 fps or 85thth

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Design VehicleDesign Vehicle

• Design Vehicle: the largest and slowest Design Vehicle: the largest and slowest

vehicle likely to use a facility with vehicle likely to use a facility with

considerable frequency.considerable frequency.

• Three Characteristics:Three Characteristics:

PhysicalPhysical

OperatingOperating

EnvironmentalEnvironmental

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Physical CharacteristicsPhysical Characteristics

• Type Passenger CarType Passenger Car MotorcycleMotorcycle TruckTruck

• Size (Several examples)Size (Several examples) LengthLength HeightHeight WeightWeight WidthWidth Minimum Turning RadiusMinimum Turning Radius

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Operating CharacteristicsOperating Characteristics

• AccelerationAcceleration

• Deceleration and brakingDeceleration and braking

• Power/weight ratiosPower/weight ratios

• Turning radiusTurning radius

• HeadlightsHeadlights

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Environmental CharacteristicsEnvironmental Characteristics

• NoiseNoise

• ExhaustExhaust

• Fuel EfficiencyFuel Efficiency

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Vehicle CharacteristicsVehicle Characteristics

• Static: those characteristics that are Static: those characteristics that are independent of the interaction with the independent of the interaction with the transportation facilitytransportation facility

• Dynamic: those characteristics that depend Dynamic: those characteristics that depend on the interaction with the transportation on the interaction with the transportation facilityfacility

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Vehicle PerformanceVehicle Performance

Impact of vehicle performance on:Impact of vehicle performance on:

• Road DesignRoad Design

• Traffic operationsTraffic operations

• Truck Performance on GradesTruck Performance on Grades

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Motion of VehiclesMotion of Vehicles

• Rectilinear motionRectilinear motion

Constant acceleration rateConstant acceleration rate

Acceleration as function of speedAcceleration as function of speed

• Motion on circular curvesMotion on circular curves

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Travel SpeedTravel Speed

12

12

tt

xxv

TimeTime

DistanceDistance

tt22tt11

xx11

xx22

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Spot SpeedSpot Speed

dt

dxv

TimeTime

DistanceDistance

tt11

xx11

VV

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Average Acceleration RateAverage Acceleration Rate

12

12

tt

vva

TimeTime

SpeedSpeed

tt22tt11

vv11

vv22

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Spot Acceleration RateSpot Acceleration Rate

dt

dva

TimeTime

SpeedSpeed

tt11

vv11aa

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Constant Acceleration MotionConstant Acceleration Motion

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ExampleExample

From the given From the given data, calculate the data, calculate the acceleration rate acceleration rate at a distance of 2’ at a distance of 2’ from the origin from the origin reference point. reference point.

DistanceDistance((ftft))

SpeedSpeed((ft/sft/s))

00 19.419.4

11 19.619.6

22 20.020.0

33 20.820.8

44 21.321.3[ a = 5.91 ft/s[ a = 5.91 ft/s2 2 ]]

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Power RequirementsPower Requirements

• Engine power required to overcome air grade, Engine power required to overcome air grade,

curve, and friction resistance to keep vehicle curve, and friction resistance to keep vehicle

in motionin motion

• Power: rate at which work is donePower: rate at which work is done

• 1 HP = 550 lb-ft/sec1 HP = 550 lb-ft/sec

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Power RequirementsPower Requirements

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Hill Climbing AbilityHill Climbing Ability

Force acting on a vehicle:Force acting on a vehicle:

• Engine PowerEngine Power

• Air ResistanceAir Resistance

• Grade ResistanceGrade Resistance

• Rolling ResistanceRolling Resistance

• FrictionFriction

• WeightWeight

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Braking on GradesBraking on Grades

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Braking DistanceBraking Distance

• DDbb = distance from brakes enact to final speed = distance from brakes enact to final speed• DDbb = f (velocity, grade, friction) = f (velocity, grade, friction)• DDbb = (V = (V00

22 – V – V22)/[30(f ± G)] (US))/[30(f ± G)] (US)oror

• Db = (VDb = (V0022 – V – V22)/[254(f ± G)] (Metric))/[254(f ± G)] (Metric)

Db = braking distance (feet or meters)Db = braking distance (feet or meters) VV00 = initial velocity (mph or kph) = initial velocity (mph or kph) V = final velocity (mph or kph)V = final velocity (mph or kph) f = coefficient of frictionf = coefficient of friction G = Grade (decimal)G = Grade (decimal) 30 or 254 = conversion coefficient30 or 254 = conversion coefficient

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Db = braking distanceu = initial velocity when applying brakesa = vehicle accelerationg = acceleration of gravity (32.2 ft/sec2)G = grade (decimal)

• AASHTO represents friction as (a/g) which is a AASHTO represents friction as (a/g) which is a function of the roadway, tires, etcfunction of the roadway, tires, etc• Can be used if deceleration is known (usually Can be used if deceleration is known (usually not) or use previous equation with frictionnot) or use previous equation with friction

Db = _____u2_____ 30({a/g} ± G)

Braking DistanceBraking Distance

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Vehicle Braking Distance

Factors:Factors:

• Braking SystemBraking System

• Tires ConditionTires Condition

• Roadway SurfaceRoadway Surface

• Initial SpeedInitial Speed

• Weather Conditions (wind, snow, etc.)Weather Conditions (wind, snow, etc.)

• GradeGrade

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Coefficient of frictionCoefficient of friction

Pavement ConditionPavement Condition MaximumMaximum SlideSlide

Good, DryGood, Dry 1.001.00 0.800.80

Good, WetGood, Wet 0.900.90 0.600.60

Poor, DryPoor, Dry 0.800.80 0.550.55

Poor, WetPoor, Wet 0.600.60 0.300.30

Snow & IceSnow & Ice 0.250.25 0.100.10

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Skid MarkSkid Mark

• A skid mark is a tire mark on the road surface A skid mark is a tire mark on the road surface produced by a tire that is locked, that is not produced by a tire that is locked, that is not rotating.rotating.

• A skid mark typically appears very light at the A skid mark typically appears very light at the beginning of the skid getting darker as the beginning of the skid getting darker as the skid progresses and comes to an abrupt end if skid progresses and comes to an abrupt end if the vehicle stops at the end of the skid. the vehicle stops at the end of the skid.

• A skid mark is left when the driver applies the A skid mark is left when the driver applies the brakes hard, locking the wheels, but the car brakes hard, locking the wheels, but the car continues to slide along the road. Steering is continues to slide along the road. Steering is not possible with the front wheels locked. Skid not possible with the front wheels locked. Skid marks are generally straight but may have marks are generally straight but may have some curvature due to the slope of the road.some curvature due to the slope of the road.

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Sight distanceSight distance

• Distance a driver can see ahead at any Distance a driver can see ahead at any

specific timespecific time

• Must allow sufficient distance for a driver Must allow sufficient distance for a driver

to perceive/react and stop when necessaryto perceive/react and stop when necessary

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Stopping Sight DistanceStopping Sight Distance

where:S = braking distancev = initial velocity when brakes are appliedG = grade (decimal)t = time to perceive/reacta = vehicle accelerationg = acceleration due to gravity (32.2 ft/sec2)

Distance to stop vehicle, includes P/R and braking distance

S = 1.47vt + _____v2_____ 30({a/g} ± G)

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where:S = braking distancev = initial velocity when brakes are appliedf = coefficient of frictionG = grade (decimal)t = time to perceive/react

With assumed acceleration, using friction

S = 1.47vt + _____v2_____ 30(f ± G)

Stopping Sight DistanceStopping Sight Distance

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SSD ExampleSSD Example

• A vehicle is traveling at uniform velocity, at tA vehicle is traveling at uniform velocity, at t00 the driver realizes a stopping vehicle in the the driver realizes a stopping vehicle in the road ahead and the driver brakes and stopsroad ahead and the driver brakes and stops

• Grade = + 1%Grade = + 1%• ttP/RP/R = 0.8 sec = 0.8 sec• The braking vehicle leaves skid marks that are The braking vehicle leaves skid marks that are

405 feet long405 feet long• Assume normal deceleration (11.2 ft/secAssume normal deceleration (11.2 ft/sec22))• Should the police office at the scene cite the Should the police office at the scene cite the

driver for traveling over the 55 mph posted driver for traveling over the 55 mph posted speed limit?speed limit?

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SSD = 1.47vt + _____v2_____ 30({a/g} ± G)

Stopping distance = 405 feet

405 feet = 1.47v(0.8 sec) +

________v2________

30({11.2/32.2} +

0.01)

405 feet = 1.17v + ________v2________

30(0.358)

405 feet = 1.17v + ________v2________

10.73

Solving for v, v = 59.9 mph

SSD ExampleSSD Example

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Motion on Circular CurvesMotion on Circular Curves

dt

dvat

R

van

2

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Motion on Circular CurvesMotion on Circular Curves

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Minimum Radius of a Circular CurveMinimum Radius of a Circular Curve

Where:Where:

• vv = vehicle velocity (mph) = vehicle velocity (mph)

• ee = tan = tan (rate of superelevation) (rate of superelevation)

• ffss = coefficient of side friction (depends on = coefficient of side friction (depends on

design speed)design speed)

)(15

2

sfe

vR

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• ExampleExample

Design speed = 65 mphDesign speed = 65 mph

Rate of superelevation = 0.05Rate of superelevation = 0.05

Coefficient of side friction = 0.11Coefficient of side friction = 0.11

• SolutionSolution

Minimum radiusMinimum radius

RRminmin = (65) = (65)22/[15(0.05+0.11)] = 1760 ft/[15(0.05+0.11)] = 1760 ft

Minimum Radius of a Circular CurveMinimum Radius of a Circular Curve

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Change Interval at Traffic SignalsChange Interval at Traffic Signals

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• Vehicle Able to Stop = D = 1.47(V)(t)+(VVehicle Able to Stop = D = 1.47(V)(t)+(V22)/30(f))/30(f)• Vehicle Travel Through = D + W + LVehicle Travel Through = D + W + L

• Change Interval (Amber) = Change Interval (Amber) = V

LWD

47.1

• Change Interval = Change Interval =

==• t = 1.0 secondt = 1.0 second

V

LWf

VVt

47.130

47.12

V

LW

f

Vt

47.1))(30(47.1

Change Interval at Traffic SignalsChange Interval at Traffic Signals

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Roadway ComponentsRoadway Components

• Roads serve four functions since they cater Roads serve four functions since they cater for:for: moving vehiclesmoving vehicles parked vehiclesparked vehicles pedestrians and non-motorized vehiclespedestrians and non-motorized vehicles allow development and access to abutting allow development and access to abutting

properties and facilitiesproperties and facilities• Functions are inherently conflicting and Functions are inherently conflicting and

inconsistent:inconsistent: ‘‘movement’ versus ‘access’movement’ versus ‘access’

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Roadway ComponentsRoadway Components

• Important design considerations:Important design considerations: CapacityCapacity SafetySafety

• Design includes:Design includes: Horizontal alignmentHorizontal alignment Vertical alignmentVertical alignment Pavement designPavement design Line marking and signageLine marking and signage