BFT40503-Chapter3a

BDD/UTHM/HANDOUT3A 1

BFT 40503

BFT 40503

ADVANCED TRAFFIC ENGINEERING Chapter 3: Intersection Signalisation

basil/uthm/2015

INTERSECTION CONTROL

An intersection is an area shared by two or more

roads.

Its main function is to allow the change of route

directions.

Intersections can be grade-separated or at-grade.

Several types of traffic control systems are used

to reduce traffic delays and crashes on at-grade

intersections, and to increase the capacity of

highways or streets.

Appropriate regulations must be enforced if these

systems are to be effective.

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CONCEPTS OF TRAFFIC CONTROL

The purpose of traffic control is to assign the right of way to drivers, and thus to facilitate highway safety by ensuring the orderly and predictable movement of all traffic on highways.

Control may be achieved by using traffic signals signs, markings that regulate, guide, warn and/or channel traffic.

To be effective, a traffic control device must:

1) Fulfill a need.

2) Command attention.

3) Convey a clear simple meaning.

4) Command respect of road users.

5) Give adequate time for proper response.

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To ensure that a traffic control device possesses

these five properties, the following factors must

be considered:

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Design

• The device should be designed with a combination of size, colour and shape that will convey a message and command the respect and attention of the driver.

Placement

• The device should be located so that it is within the cone of vision of the viewer and the driver has adequate response time when driving at normal speed.

Operation

• The device should be used in a manner that ensures the fulfilment of traffic requirements in a consistent and uniform way.


BFT 40503


To ensure that a traffic control device possesses

these five properties, the following factors must

be considered:

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Maintenance

•The device must be regularly maintained to ensure that legibility is sustained.

Uniformity

•To facilitate the recognition and understanding of these devices by drivers, similar devices should be used at locations with similar traffic and geometric characteristics.

TYPES OF INTERSECTION CONTROL

The primary objective in the design of traffic

control system at an intersection is to reduce the

number of significant conflict points.

The methods selected for controlling conflicting

streams of vehicles at intersections depend on:

the type of intersection

the volume of traffic in each conflicting

streams

The two types of intersection control are:

(1) Yield signs

(2) Stop signs

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YIELD SIGN CONTROL

All drivers on approaches with yield signs are required to slow down and yield the right of way to all conflicting vehicles at the intersection.

Stopping at yield sign is not mandatory, but drivers are required to stop when necessary to avoid interfering with a traffic stream that has the right of way.

Yield signs are therefore placed on minor-road approaches, where it is necessary to yield the right of way to the major-road traffic.

This sign is warranted at intersections where there is a separate or channelised left-turn lane without an adequate acceleration lane. 7

STOP SIGN CONTROL

A stop sign is used where an approaching vehicle is required to stop before entering the intersection.

Stop signs should be used only when they are warranted, since the use of these signs results in inconvenience to motorists.

Stops signs should not be used at signalised intersections or on through roadways of expressways.

The warrants for stop signs suggest that a stop sign may be used:

1. On a minor road when it intersects a major road

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BFT 40503

STOP SIGN CONTROL

2. At an unsignalised intersection.

3. Where a combination of high speed, restricted

view and serious crashes indicates the

necessity for such a control.

“Multiway stop signs” require that all vehicles

approaching the intersection stop before entering

it.

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STOP SIGN CONTROL

Multiway stop signs are used as a safety measure

at some intersections and are normally used

when the traffic volumes on all approaches are

approximately equal. When volumes are high,

the use of signals is recommended.

The warrants of multiway control specify that the

total intersection approach volume should not be

less than 500 veh/h for 8 hr of an average day,

nor should the combine volume of vehicles and

pedestrians from the minor approach be less than

200 units per hour for the same 8 hr. The average

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STOP SIGN CONTROL

delay of the vehicles on the minor street also

should not be less than 30 sec per vehicle during

the maximum hour.

The minimum requirement for vehicular volume

can be reduced by 30% if the 85th percentile

approach speed on the major approach is > 40

mph (64.4 km/h)

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STOP SIGN CONTROL

Example 3.1

A minor road carrying 150 veh/h for 8 hr of an

average day crosses a major road carrying 320 veh/h

for the same 8 hr, forming a four-leg intersection.

Determine whether a multiway stop sign is justified at

this location if the following conditions exist:

The pedestrian volume from the minor street for the

same 8 hr as the traffic volumes is 70 ped/hr.

The average delay to minor-street vehicular traffic

during the maximum hours is 37 sec per vehicle.

The 85th percentile approach speed of the major

road is 43 mph. 12


BFT 40503

STOP SIGN CONTROL

Solution

The warrant is that the total intersection volume

should not be less than 500 veh/h for 8 hr.

Total vehicular volume = 150 + 320 = 470 veh/h.

But, since the 85th percentile speed > 40 mph, the

requirement can be reduced by 30%. The total

volume required now is not less than 350 veh/h.

This satisfies the vehicular volume requirement. 13

STOP SIGN CONTROL

The warrant stipulates that average delay of vehicles on the minor street should not be less than 30 sec per vehicle during the maximum hour.

This is satisfied because the measured average delay was 37 sec per vehicle.

The warrant also stipulates that the combined vehicular and pedestrian traffic on the minor street should not be less than 200 units per hour.

This is satisfied because the combined traffic is 150 + 70 = 220 units per hour.

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TRAFFIC SIGNALS

One of the most effective ways of controlling

traffic at an intersection is the use of traffic

signals.

The significant factors that determine the need

for traffic signals at a particular intersection are:

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WARRANTS FOR TRAFFIC SIGNALS

The Manual on Uniform Traffic Control Devices (MUTCD) details 11 warrants, at least one of which should be satisfied for an intersection to be signalised.

8-hour vehicular volume

o Minimum vehicular volume

o Interruption of continuous traffic

o Combination of warrants

Minimum pedestrian volume

School crossing

Coordinated signal system

Crash experience

Roadway network

4-hour vehicular volume

Peak hour

o Peak hour delay

o Peak hour volume 16


BFT 40503


1. Minimum Vehicle Volume

This warrant is applied when the principal factor

for considering signalisation is the traffic volume.

The warrant is satisfied when traffic volumes on

major streets and on higher-volume minor street

approaches for each of any 8hr of are at least

equal to the volumes in the Table 1.

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Table 1: Volume requirements for Minimum

Vehicular Volumes Warrant

Note: If posted, statutory or 85th percentile speed on the major street is > 40

mph (64.4 km/h) or if the intersection lies in an area with population

<10,000, 70% of the volumes shown may be used.

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Number of Lanes for

Moving Traffic on

Each Approach

Vehicles per

hour on Major

Street (total of

both

approaches)

Vehicles per hour

on Higher Volume

Minor Street

Approach (one

direction)

Major

Street

Minor

Street

1

≥ 2

≥ 2

1

1

1

≥ 2

≥ 2

500

600

600

500

150

150

200

200


2. Interruptions of Continuous Traffic

This warrant should be considered when traffic

on a minor street experiences excessive delay due

to heavy volume on the major street.

Heavy major street traffic may also make it

hazardous for minor-street traffic to enter or

cross the major street.

The warrant is satisfied when the traffic volume

on the major street and on the higher-volume

minor street approach for each of any 8 hr of an

average day is at least equal to the volumes in

Table 2. 19


Table 2: Minimum Vehicular Volumes for

Interruption of Continuous Traffic Warrant

Note: If posted, statutory or 85th percentile speed on the major street is > 40

mph (64.4 km/h) or if the intersection lies in an area with population

<10,000, 70% of the volumes shown may be used.

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Number of Lanes for

Moving Traffic on

Each Approach

Vehicles per

hour on Major

Street (total of

both

approaches)

Vehicles per hour

on Higher Volume

Minor Street

Approach (one

direction)

Major

Street

Minor

Street

1

≥ 2

≥ 2

1

1

1

≥ 2

≥ 2

750

900

900

750

75

75

100

100


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3. Combination of Warrants

This warrant, in exceptional cases, justifies the

installation of signals when none of the above

warrants is satisfied but when the first two

warrants are satisfied to the extent of 80% of the

stipulated volumes, i.e. volumes given in Tables 1

and 2.

4. Minimum Pedestrian Volume

This warrant is satisfied when the pedestrian

volume crossing the major street on an average

day is at least 100 ped for each of any 4 hr, or 21


190 ped during any 1 hr, and there are fewer than 60 gaps per hour that are acceptable by pedestrians for crossing.

In addition, the nearest traffic signal along the major street should be at least 300 ft (91.4 m) away from the intersection.

When this warrant is used, the signal should be the traffic-actuated type, with push buttons.

5. School Crossing

When an analysis of gap data at an established school zone shows that the frequency of occurrence of gaps and the lengths of gaps are 22


inadequate for safe crossing by schoolchildren,

this warrant is applied.

Traffic signals are warranted during the period

when schoolchildren are using the crossing the

no. of acceptable gaps is < 4, and there are at

least 20 students during the highest crossing

hour.

The signal used is pedestrian-actuated, and all

obstructions to view should be prohibited for at

least 100 ft (30.5 m) before and 20 ft (6 m) after

the crosswalk. 23


6. Coordinated Signal System

This warrant may justify the installation of

traffic lights at an intersection where lights

would not otherwise have been installed.

It justifies that such an installation will help

maintain a proper grouping of vehicles and

effectively regulate group speed.

This warrant is not applicable when the

resultant spacing of the traffic signal will be less

than 300 ft (91.4 m).

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BFT 40503


7. Crash Experience

This warrant justifies signalisation of an

intersection when crash frequency has not been

reduced by adequate trial of less restrictive

measures.

It stipulates that the use of traffic signals is

warranted at an intersection if 5 or more injury

or reportable property-damage-only crashes have

occurred within a 12-month period and that

signal control is a suitable countermeasure for

these crashes.

In addition, the traffic and pedestrian volumes 25


should not be less than 80% of the requirements

specified in Warrants 1, 2 and 4.

8. Roadway Network

This warrant justifies the installation of signals

at some intersections when such an installation

will help to encourage concentration and

organisation of traffic networks.

The warrant can be applied at intersections of

two or more major roads when:

(1) The total existing or immediately projected

entering volume is at least 1,000 during the peak 26


hour of a typical weekday, and the 5-year

projected traffic volumes, based on an

engineering study, satisfy the requirements of

the following warrants:

Maximum vehicular volume

Interruption of traffic

Combination of warrants

4-hr volume

Peak hour volume

(2) When the total existing or projected entering

volume is at least 1,000 vehicles for each of any

5-hr of a Saturday and/or a Sunday. 27


9. Four-Hour Volume

This warrant is based on Figure 1.

When the plot for each of any 4 hr of an average

day falls above the standard graph, this warrant

is satisfied.

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BFT 40503


Figure 1: Graphs for Four-Hour Volume Warrant

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10. Peak-Hour Delay

This warrant is used to justify the installation of

traffic signals at intersections where traffic

conditions during 1 hr of the day result in undue

delay on the minor street.

The warrant is satisfied when the delay during

any four consecutive 15-min periods on one of the

minor-street approaches (one direction only)

controlled by a stop sign is equal to or greater

than specified levels and the same minor-street

approach (one direction only) volume and the

total intersection entering volume are equal to 30


or greater than the specified levels.

The specified delay is 4 vehicle-hours for a one-

lane approach and 5 vehicle-hours for a two-lane

approach.

The specified volumes are 100 veh/h for one

moving lane for intersections with four or more

approaches or 650 veh/h for intersections with

three approaches.

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11. Peak-Hour Volume

This warrant is also used to justify the

installation of traffic signals at intersections

where traffic conditions during 1 hr of the day

result in undue delay on the minor street.

It is based on Figure 2.

When the plot for an average day lies above the

standard curve, this warrant is satisfied.

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BFT 40503


Figure 2: Graphs for Peak-Hour Volume Warrant

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Example 3.2

A two-lane minor street crosses a four-lane major

street. If the traffic conditions are as given below,

determine whether installing a traffic signal at this

intersection is warranted.

The traffic volumes for each of 8 hr of an average

day (both directions on major street) total 400

veh/h. For the higher-volume minor street (one

direction) the total is 100 veh/h.

The 85th percentile speed of major-street traffic is

43 mph (69.2 km/h). 34


The pedestrian volume crossing the major street

during an average day is 200 ped/hour during peak

pedestrian periods (2 hr in the morning, 2 hr in the

afternoon)

The number of acceptable gaps per hour in the

traffic stream for pedestrians to cross during peak

pedestrian periods is 62.

The nearest traffic signal is located 450 ft (137 m)

from this location.

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Solution

Since vehicular and pedestrian volumes are known,

check the following warrants:

1. Minimum vehicle volume (Warrant 1)

2. Minimum pedestrian volume (Warrant 4)

Min. volume requirements (two-lanes for major

street and one lane for minor street) from Table 1:

600 veh/h on major (total of both approaches)

150 veh/h on minor (one direction) 36


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Number of Lanes for

Moving Traffic on

Each Approach

Vehicles per

hour on Major

Street (total of

both

approaches)

Vehicles per hour

on Higher Volume

Minor Street

Approach (one

direction)

Major

Street

Minor

Street

1

≥ 2

≥ 2

1

1

1

≥ 2

≥ 2

500

600

600

500

150

150

200

200

Since the 85th percentile speed is greater than 40 mph, the requirements can be reduced to 70%. Thus,

420 veh/h on major (total of both approaches)

105 veh/h on minor (one direction)


Unfortunately, the current traffic volumes do not meet

the minimum requirements, i.e.

400 < 420 veh/h on major

100 < 105 veh/h on minor

Therefore Warrant 1 is not satisfied.

Min. pedestrian volume requirements:

100 or more (each day of any 4 hr)

190 or more (any 1 hr)

The current pedestrian volume is 200 (4 hr peak

periods). Therefore Warrant 4 is satisfied. 38


Warrant 4 also mentions requirement for acceptable gaps (i.e. minimum 60 gaps per hour) and location of nearest traffic signal (i.e. minimum 300 ft)

The number of available acceptable gaps is 62, which satisfies the requirement.

The nearest traffic signal is located 450 ft, therefore it satisfies the requirement.

Conclusion: A traffic signal is justified under Warrant 4 (minimum pedestrian volume). The signal should be traffic-actuated type with push buttons for pedestrians. 39

ACTUATED TRAFFIC SIGNALS

A major disadvantage of fixed or pre-timed signals is that they cannot adjust themselves to handle fluctuating traffic volumes.

When fluctuation of traffic volumes warrants it, a vehicle-actuated signal is used. These signals are capable of adjusting themselves.

When actuated signals are used, vehicles arriving at the intersection are detected by detectors, which transmit this information to a controller unit.

The controller then adjusts the phase lengths to meet the requirements of prevailing traffic conditions. 40


BFT 40503


Actuated signals can be either:

(1) Semi-actuated

(2) Fully actuated

1. Semi-Actuated Signals

Semi-actuated signals are used when the major

stream flow is uniform and the minor stream

flow is low.

The detectors are placed only in the minor

stream flow.

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The semi-actuated signals are set as follows:

(1) The green signal on the major approach is

preset for a minimum period, but it will stay on

until the signal is actuated by a minor-street

vehicle.

(2) If the green signal on the major approach

has been on for a period equal to or greater than

the minimum, the signal will change to red in

response to the actuation of the minor-street

vehicle.

(3) The green signal on the minor stream will

then come on for at least a period equal to the

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minimum for this stream.

(4) The signal on the minor stream then

changes to red, and that on the major stream

changes to green.

If volume is high on the minor-street, the signal

will act as a pre-timed signal.

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2. Fully Actuated Signals

Fully actuated signals are suitable for

intersections at which large fluctuations of traffic

volumes occur on all approaches during the day.

Maximum and minimum green times are set for

each approach.

The green time on one approach (say, north-south

direction) will stay on until the minimum green

time ends. If vehicles actuate the detectors on the

other approach (say, east-west direction), then a

red signal will come on for the north-south

approach. If there are no vehicles arriving on 44


BFT 40503


the east-west approach, the north-south

approach will continue to experience green until

the maximum green time expires.

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46

Controller

Detector

Traffic lights


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BFT40503-Chapter3a

Documents

traffic control device

concepts of traffic

purpose of traffic control

similar traffic

volume of traffic

traffic delays

traffic stream

yield sign control