ECGD 4121 – Transportation Engineering IECGD 4121 – Transportation Engineering I

Lecture 8Lecture 8

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

Civil Engineering DepartmentCivil Engineering Department

11stst Semester 2009/2010 Semester 2009/2010

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Intersections Design & ControlIntersections Design & Control

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ContentContent

IntersectionsIntersections

• InterchangesInterchanges

• Grade-separated intersectionsGrade-separated intersections

• At-grade intersectionsAt-grade intersections

ChannelizationChannelization

• Clearly defined travel paths for vehiclesClearly defined travel paths for vehicles

InterchangesInterchanges

Ramps at different levels connecting two or Ramps at different levels connecting two or more freewaysmore freeways

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Grade-separated IntersectionsGrade-separated Intersections

Two intersecting highways connected at Two intersecting highways connected at different elevationsdifferent elevations

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Two intersecting roads connected at the same Two intersecting roads connected at the same elevationelevation

At-grade IntersectionsAt-grade Intersections

At-grade IntersectionsAt-grade Intersections

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Two intersecting roads connected at the same Two intersecting roads connected at the same elevationelevation

Objectives of Traffic ChannelizationObjectives of Traffic Channelization

• To establish clear definition of vehicle pathsTo establish clear definition of vehicle paths

• To control movement of trafficTo control movement of traffic

• To provide safe refuge for pedestriansTo provide safe refuge for pedestrians

• To separate traffic conflictsTo separate traffic conflicts

• To provide safe merging/diverging of trafficTo provide safe merging/diverging of traffic

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Channelized IntersectionsChannelized Intersections

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• Objective: to reduce the conflict points at an Objective: to reduce the conflict points at an intersectionintersection

• Method of control depends on:Method of control depends on:Type of intersection (4-way, T-Intersection, Type of intersection (4-way, T-Intersection,

etc.)etc.)Traffic volume in each conflicting streamTraffic volume in each conflicting stream

• Guidelines provided in Manual on Uniform Guidelines provided in Manual on Uniform Traffic Control Devices (MUTCD)Traffic Control Devices (MUTCD)

• Guidelines presented in the form of warrants Guidelines presented in the form of warrants (i.e. conditions that call for intersection (i.e. conditions that call for intersection control)control)

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Intersections ControlIntersections Control

Intersection Control Using Yield SignsIntersection Control Using Yield Signs

• Eliminates crossing conflictsEliminates crossing conflicts

• Used at major road-minor road intersectionsUsed at major road-minor road intersections

• Warrants:Warrants:

Approach speed on minor road > 10 mphApproach speed on minor road > 10 mph

When there is a separate channelized lane When there is a separate channelized lane

without adequate acceleration lanewithout adequate acceleration lane

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• Eliminates crossing & merging conflictsEliminates crossing & merging conflicts• Inconvenient to motoristsInconvenient to motorists• Used where approaching vehicle has to stop Used where approaching vehicle has to stop

before the intersectionbefore the intersection• Warrants:Warrants:

Minor road intersects with major roadMinor road intersects with major roadPresence of hazardous conditions such as Presence of hazardous conditions such as

high approach speed, restricted view, and high approach speed, restricted view, and history of accidentshistory of accidents

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Intersection Control Using Stop SignsIntersection Control Using Stop Signs

• Used when traffic volumes on all approaches are Used when traffic volumes on all approaches are approximately equalapproximately equal

• For too high traffic volumes, use signalsFor too high traffic volumes, use signals• Warrants: (satisfy all)Warrants: (satisfy all)

Total int. approach volume > 500 vph for any 8 Total int. approach volume > 500 vph for any 8 hours of average dayhours of average day

Combined vehicle + pedestrian volume for Combined vehicle + pedestrian volume for minor approach > 200 units per hour for same minor approach > 200 units per hour for same 8-hr. period8-hr. period

Avg. vehicle delay on minor street > 30 sec/veh Avg. vehicle delay on minor street > 30 sec/veh for max. hrfor max. hr

If 85If 85thth percentile approach speed on major percentile approach speed on major approach is > 40 mphapproach is > 40 mph

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Intersection Control Using Multi-Way Stop SignsIntersection Control Using Multi-Way Stop Signs

• When minor road traffic suffers excessive When minor road traffic suffers excessive delaysdelays

• Minimum pedestrian volume:Minimum pedestrian volume:Ped. Volume crossing major street > 100 for Ped. Volume crossing major street > 100 for

any 4 hrsany 4 hrsPed. Volume crossing major street > 190 for Ped. Volume crossing major street > 190 for

any 1 hrany 1 hrTraffic leaves less than 60 gaps accepted by Traffic leaves less than 60 gaps accepted by

pedestrians per hourpedestrians per hourNearest traffic signal > 300 ft. awayNearest traffic signal > 300 ft. awayUse traffic actuated signal, push button Use traffic actuated signal, push button

operation for pedestriansoperation for pedestrians14

Intersection Control Using Traffic SignalsIntersection Control Using Traffic Signals

• School crossingsSchool crossings Used when traffic gaps are inadequate for safe Used when traffic gaps are inadequate for safe

crossingcrossing When no. of accepted gaps < minutes in periodWhen no. of accepted gaps < minutes in period No parking within 100 ft. before and 20 ft. after No parking within 100 ft. before and 20 ft. after

crossingcrossing• Progressive movementProgressive movement

Exception to other warrants when it helps to Exception to other warrants when it helps to maintain grouping of vehicles to regulate the group maintain grouping of vehicles to regulate the group speedspeed

• Accident experience (when signal is suitable)Accident experience (when signal is suitable) 5 or more injury in 12 months5 or more injury in 12 months

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Intersection Control Using Traffic SignalsIntersection Control Using Traffic Signals

• Peak hour delay: delay and volume in any 4 Peak hour delay: delay and volume in any 4

consec. 15-min periods when controlled by stop consec. 15-min periods when controlled by stop

sign is:sign is:

> 4 veh-hrs & 100 vph for 2-lane minor street > 4 veh-hrs & 100 vph for 2-lane minor street

approachapproach

> 5 veh-hrs & 150 vph for 2-lane minor street > 5 veh-hrs & 150 vph for 2-lane minor street

approachapproach

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Intersection Control Using Traffic SignalsIntersection Control Using Traffic Signals

Signal Timing - TerminologySignal Timing - Terminology

• Controller - fixed or variable timingController - fixed or variable timing

• Cycle (one complete color sequence)Cycle (one complete color sequence)

• Phase-part of cycle allocated to a stream of trafficPhase-part of cycle allocated to a stream of traffic

• Interval - part of cycle when indications do not Interval - part of cycle when indications do not changechange

• Offset - time lapse between green @ successive Offset - time lapse between green @ successive intersectionsintersections

• Change & clearance interval - Total time in seconds Change & clearance interval - Total time in seconds for yellow & all-red signal indicationsfor yellow & all-red signal indications

• All-red interval - when display is red for all directionsAll-red interval - when display is red for all directions

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Two-Phase SignalTwo-Phase Signal

• Phase (A)Phase (A)East-West Through Movement has Right-East-West Through Movement has Right-

of-Wayof-Way

• Phase (B)Phase (B)North-South Through Movement has Right-North-South Through Movement has Right-

of-Wayof-Way

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Two-Phase Signal: Phase (A)Two-Phase Signal: Phase (A)

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Two-Phase Signal: Phase (B)Two-Phase Signal: Phase (B)

• Phase APhase A East-West Left Turn Movement has Right-of-WayEast-West Left Turn Movement has Right-of-Way

• Phase BPhase B East-West Through Movement has Right-of-WayEast-West Through Movement has Right-of-Way

• Phase CPhase C North-South Left Turn Movement has Right-of-North-South Left Turn Movement has Right-of-

WayWay• Phase DPhase D

North-South Through Movement has Right-of-North-South Through Movement has Right-of-WayWay

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Four-Phase SignalFour-Phase Signal

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Four-Phase Signal: Phase (A)Four-Phase Signal: Phase (A)

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Four-Phase Signal: Phase (B)Four-Phase Signal: Phase (B)

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Four-Phase Signal: Phase (C)Four-Phase Signal: Phase (C)

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Four-Phase Signal: Phase (D)Four-Phase Signal: Phase (D)

Reduction in ConflictsReduction in ConflictsDue to Traffic SignalDue to Traffic Signal

No SignalNo Signal 2-Phase2-Phase 4-4-

PhasePhase

Crossing ConflictsCrossing Conflicts 1616 44 00

Merge ConflictsMerge Conflicts 8 8 88 88

Diverging ConflictsDiverging Conflicts 8 8 88 44

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Example 1Example 1

A section of a major highway has a speed-flow A section of a major highway has a speed-flow

relationship of the form:relationship of the form:

q = auq = au22 + bu + bu

It is known that the capacity is 2925 veh/hr and It is known that the capacity is 2925 veh/hr and

the corresponding space-mean speed of traffic is the corresponding space-mean speed of traffic is

30 mph. Determine the speed when the flow is 30 mph. Determine the speed when the flow is

1400 veh/hr and the free-flow speed. 1400 veh/hr and the free-flow speed. 

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Example 1 - SolutionExample 1 - Solution

@ q@ qmm = 2925 veh/hr, u = 2925 veh/hr, umm = 30 mph = 30 mph

@ q@ qmm, dq/du = 0, dq/du = 0

dq/du = 2audq/du = 2aumm + b = 0 + b = 0

(2)(a)(30) + b = 0 ……………... [1](2)(a)(30) + b = 0 ……………... [1]

qqmm = au = aumm22 + bu + bu

2925 = (a)(30)2925 = (a)(30)22 + (b)(30) …….. [2] + (b)(30) …….. [2]

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Example 1 - SolutionExample 1 - Solution

Solving for a & b Solving for a & b

a = -3.25 & b = 195.00a = -3.25 & b = 195.00

q = -3.25uq = -3.25u22 + 195u + 195u

@ q = 1400 veh/hr,@ q = 1400 veh/hr,

1400 = -3.25u1400 = -3.25u22 + 195u + 195u

Solving for u Solving for u

uu11 = 8 veh/hr & u = 8 veh/hr & u22 = 52 = 5229

Example 1 - SolutionExample 1 - Solution

@ u@ uff, q = 0 , q = 0

0 = -3.25u0 = -3.25uff22 + 195u + 195uff

Solving for uSolving for uff

uuff = 60 veh/hr = 60 veh/hr

OROR

uuff = 2u = 2umm = (2)(30) = 60 veh/hr = (2)(30) = 60 veh/hr

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Example 2Example 2

A section of a major highway has the following A section of a major highway has the following

flow-density relationship:flow-density relationship:

q = 42k-0.56kq = 42k-0.56k22

What is the capacity of the highway section, and What is the capacity of the highway section, and

the speed when the highway is at one quarter of the speed when the highway is at one quarter of

its capacity.its capacity.

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Example 2- SolutionExample 2- Solution

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@ Capacity, q = q@ Capacity, q = qmm , k = k , k = kmm, and u = u, and u = umm

@ q@ qmm, dq/du = 0, dq/du = 0

dq/du = 42 - 1.12kdq/du = 42 - 1.12kmm = 0 = 0

kkmm = 42/1.12 = 37.50 veh./mile = 42/1.12 = 37.50 veh./mile

Capacity = qCapacity = qmm = 42k = 42kmm – 0.56k – 0.56kmm22

Capacity = qCapacity = qmm = 787.5 veh./hr. = 787.5 veh./hr.

Example 2- SolutionExample 2- Solution

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@ One-quarter of capacity,@ One-quarter of capacity,

q = qq = qmm /4 = 196.875 veh./hr. /4 = 196.875 veh./hr.

q = 196.875 = 42k – 0.56kq = 196.875 = 42k – 0.56k22

0.56k0.56k22 - 42k + 196.875 = 0 - 42k + 196.875 = 0

Solving for k values,Solving for k values,

kk11 = 5 veh./mile OR k = 5 veh./mile OR k22 = 70 veh./mile = 70 veh./mile

Example 2- SolutionExample 2- Solution

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@ q = 196.875 veh./hr. & k@ q = 196.875 veh./hr. & k11 = 5 veh./mile, = 5 veh./mile,

Speed = uSpeed = u11 = q/k = q/k11 = 39.375 mph = 39.375 mph

OROR

@ q = 196.875 veh./hr. & k@ q = 196.875 veh./hr. & k22 = 70 veh./mile, = 70 veh./mile,

Speed = uSpeed = u22 = q/k = q/k22 = 2.8125 mph = 2.8125 mph