Lec 03 Intersection Control

Faculty of Engineering ‐ 3rd Year 35

Traffic Eng. Intersection Control 15 –16

Dr. Firas H. Asad

In this lecture; ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ 1‐ Concepts of Traffic Control

2‐ Conflict Points

3‐ Types of Intersection Control

4‐ Warrants of Traffic Signal

At‐Grade Intersection Control السيطرة على التقاطعات

The information included in this lecture is largely taken from Traffic and Highway Engineering (Garber and Hoel, 2009) and A Policy on Geometric Design of Highways and Streets (AASHTO, 2011) and Manual on Uniform Traffic Control Devices (MUTCD, 2012).

1‐ Concepts of Traffic Control مبادئ السيطرة المرورية

The flow of traffic on any street or highway is greatly affected by the flow of traffic

through the intersection points on that street or highway because the intersection

usually performs at a level مستوى اداء below that of any other section of the road.

According to Garber and Hoel (2009) and other researchers, several types of traffic‐

control systems are used to reduce traffic delays and accidents on at‐grade

intersections and to increase the capacity of highways and streets. However,

appropriate regulations must be enforced تفرض if these systems are to be effective.

This lecture describes the different methods of controlling traffic on at‐grade

intersections.

The purpose of traffic control is to assign د to drivers and حق المرور the right of way تحدي

thus to facilitate د تاكي highway safety by ensuring the orderly and predictable



Dr. Firas H. Asad

movement of all traffic on highways. Control may be achieved by using traffic

signals, signs, or markings that regulate, guide, warn, and/or channel traffic.

Guidelines for determining whether a particular control type is suitable for a given

intersection are provided in the Manual on Uniform Traffic Control Devices (MUTCD,

2012). To ensure that a traffic‐control device is effective the MUTCD recommends

that engineers consider the following five factors:

1. Design. The device should be designed with a combination of size, color, and

shape that will convey توصل a clear message and command تستجلب the respect and

attention of the driver.

2. Placement. The device should be located ا so that it is within the cone of يحدد موقعه

vision of the viewer and the driver has adequate response time when driving at

normal speed.

3. Operation. The device should be used in a manner that ensures the fulfilment ق تحق

of traffic requirements in a consistent and uniform way.

4. Maintenance. The device must be regularly maintained to ensure that legibility

.تستدام is sustained وضوح القراءة

5. 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.

2‐ Conflict Points at Intersections

Conflicts occur when traffic streams moving in different directions interfere داخل with يت

each other. The three types of conflicts are merging اء ,االلتق diverging راق ,االفت and

crossing اطع .التق Figure below shows the different conflict points that exist at a four‐

approach unsignalized intersection. There are 32 conflict points in this case.



Dr. Firas H. Asad

The number of possible conflict points at any intersection depends on the number

of approaches, the turning movements, and the type of traffic control at the

intersection. The primary objective in the design of a traffic‐control system at an

intersection is to reduce the number of significant conflict points. In designing such

a system, it is first necessary to undertake an analysis of the turning movements at

the intersection which will indicate the significant types of conflicts. Factors that

influence the significance of a conflict include the type of conflict, the number of

vehicles in each conflicting stream, and the speeds of the vehicles in those streams.

Crossing conflicts, however, tend to have the most severe effect on traffic flow and

should be reduced to a minimum whenever possible (Garber and Hoel, 2009).

3‐ Types of Intersection Control

Several methods of controlling conflicting streams of vehicles at intersections are in

use. The choice of one of these methods depends on the type of intersection and

the volume of traffic in each of the conflicting streams. Guidelines for determining

whether a particular control type is suitable for a given intersection have been



Dr. Firas H. Asad

developed and are given in the MUTCD. These guidelines are presented in the form

of warrants ررات ,مب which have to be compared with the traffic and geometric

characteristics at the intersection being considered. The different types of

intersection control are described here.

3.1 Yield Signs عالمات حق المرور

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 signs is

not mandatory ا يس واجب ,ل 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

usually placed on minor‐road approaches, where it is necessary to yield the right of

way to the major road traffic. Figure below shows the regulated shape and

dimensions for a yield sign. The most significant factor in the warrant for yield signs

is the approach speed on the minor road. This sign is warranted at intersections

where there is a separate or channelized right‐turn lane without an adequate

acceleration lane.



Dr. Firas H. Asad

3.2 Stop Signs

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

the intersection. Figure below shows the regulated shape and dimensions of a stop

sign. Stop signs should be used only when they are warranted, since the use of these

signs results in considerable inconvenience to motorists. Stop signs should not be

used at signalized intersections or on through roadways of expressways.

The warrants for stop signs suggest that a stop sign may be used on a minor road

when it intersects a major road, at an unsignalized intersection, and where a

combination of high speed, restricted view, and serious crashes indicates the

necessity for such a control.



Dr. Firas H. Asad

3.3 Multiway Stop Signs

Multiway stop signs require that all vehicles approaching the intersection stop

before entering it. They are used as a safety measure at some intersections and

normally are used when the traffic volumes on all of the approaches are

approximately equal. When traffic volumes are high, however, the use of signals is

recommended. They should also be considered when five or more crashes occur at

an intersection in a 12‐month period, and these crashes could be avoided with a

multiway stop control. The volume warrants for this control specify that the total

volume on both major street approaches should not be less than 300 veh/h for any

eight hours of an average day, nor should the combined volume of vehicles and

pedestrians from the minor approaches be less than 200 units/h for the same eight

hours. The average delay of the vehicles on the minor street should also be not less

than 30 sec/veh during the maximum hour.

The minimum requirement for vehicular volume can be reduced by 30 percent if the

85th‐percentile approach speed on the major approach is greater than 40 mi/h.

Also, if none of the safety or volume criteria ددات مح (excluding that for the 30

percent reduction for speeds of 40 mi/h or more) is fully met, but each satisfies 80

percent of the minimum requirement, the installation of a multiway stop sign is

justified يبرر .



Dr. Firas H. Asad



Dr. Firas H. Asad

3.4 Intersection Channelization

As explained in the previous lecture, intersection channelization is used mainly to

separate turn lanes from through lanes. A channelized intersection consists of solid

white lines or raised barriers which guide traffic within a lane so that vehicles can

safely pass through a complex intersection. When raised islands are used, they can

also provide a refuge for pedestrians.

3.5 Traffic Signals

One of the most effective ways of controlling traffic at an intersection is the use of

traffic signals. Traffic signals can be used to eliminate اثير اء ت many conflicts because الغ

different traffic streams can be assigned the use of the intersection at different

times. Since this results in يسبب a delay to vehicles in all streams, it is important that

traffic signals be used only when necessary. The most important factor that

determines the need for traffic signals at a particular intersection is the

intersection’s approach traffic volume, although other factors such as pedestrian

volume and crash experience may also play a significant role.



Dr. Firas H. Asad

4‐ Warrants of Traffic Signals مبررات نصب االشارات المرورية الضوئية The Manual on Traffic Signal Design gives the fundamental concepts and standard

practices used in the design of traffic signals. In addition, the MUTCD describes eight

warrants in detail, at least one of which should be satisfied for an intersection to be

signalized. However, these warrants should be considered only as a guide.

Professional judgment based on experience also should be used to decide whether

or not an intersection should be signalized. The factors considered in the warrants

are:

• Warrant 1 ‐ Eight‐hour vehicular volume

• Warrant 2 ‐ Four‐hour vehicular volume

• Warrant 3 ‐ Peak hour

• Warrant 4 ‐ Pedestrian volume

• Warrant 5 ‐ School crossing

• Warrant 6 ‐ Coordinated signal system نظام اشارة ضوئية منسق

• Warrant 7 ‐ Crash experience الحوادث حالة

• Warrant 8 ‐ Roadway network

According to MUTCD (2012), a traffic control signal should not be installed unless

one or more of the factors described in this Chapter are met. A traffic control signal

should not be installed unless an engineering study indicates that installing a traffic

control signal will improve the overall safety and/or operation of the intersection.

Also, a traffic control signal should not be installed if it will seriously disrupt

progressive التتابعي traffic flow.

Following is a brief discussion of each of these warrants according to MUTCD (2012)

and Garber and Hoel (2009).



Dr. Firas H. Asad

Warrant 1 ‐ Eight‐Hour Vehicular Volume

The need for a traffic control signal shall be considered if an engineering study finds

that at least one of the following conditions (A or B) exist for each of any 8 hours of

an average day:

Condition A (Minimum Vehicular Volume): This condition is intended for

application at locations where a large volume of intersecting traffic is the

principal الرئيسي reason to consider installing a traffic control signal. The warrant is

satisfied when traffic volumes on the major‐street and the higher volume minor‐

street approaches for each of any eight hours of an average day are at least equal to

the volumes specified in the 100 percent columns of Table 1‐A. An “average” day is a

weekday whose traffic volumes are normally and repeatedly observed at the

location.

Condition B (Interruption of Continuous Flow): This condition is intended for

application at locations where Condition A is not satisfied and where the traffic



Dr. Firas H. Asad

volume on a major street is so heavy that traffic on a minor intersecting street

suffers excessiveالي ع delay or conflict in entering or crossing the major street. The

warrant is satisfied when traffic volumes on the major‐street and on the higher

volume minor‐street approaches for each of any eight hours of an average day are

at least equal to the volumes specified in the 100 percent columns of Table 1‐B.

In applying each condition the major‐street and minor‐street volumes shall be for

the same 8 hours. On the minor street, the higher volume shall not be required to

be on the same approach during each of these 8 hours.

Also, if both Conditions A and B are not satisfied, and other remedial actions اجراءات

ة have been taken without much success, the 80, 70, or 56 percent column may عالجي

be used, as indicted in Tables 1.

Warrant 2 ‐ Four‐Hour Vehicular Volume

The Four‐Hour Vehicular Volume signal warrant conditions are intended to be

applied where the volume of intersecting traffic is the principal reason to consider

installing a traffic control signal. The need for a traffic control signal shall be

considered (warranted) if an engineering study finds that, for each of any 4 hours of

an average day, the plotted points representing the vehicles per hour on the major

street (total of both approaches) and the corresponding vehicles per hour on the

higher‐volume minor‐street approach (one direction only) all fall above the

applicable curve in Figure 2 (see next page) for the existing combination of approach

lanes. On the minor street, the higher volume shall not be required to be on the

same approach during each of these 4 hours.

The MUTCD manual suggest using another Figure if the posted speed limit or the

85th‐percentile speed on the major street exceeds 40 mph, or if the intersection lies



Dr. Firas H. Asad

within the built‐up ة area of an isolated community having a population of less المأهول

than 10,000.

Warrant 3 ‐ Peak Hour

The Peak Hour ذروة warrant of installation a traffic signal is intended for use at ساعة ال

a location where traffic conditions are such that for a minimum of 1 hour of an

average day result undue ر مرغوب اضافي غي delay on the minor‐street traffic when

entering or crossing the major street. This signal warrant shall be applied only in

unusual cases, such as office complexes ات ,محطات تصنيع manufacturing plants ,المجمع

industrial complexes, or high‐occupancy vehicle facilities that attract or discharge

large numbers of vehicles over a short time.

The need for a traffic control signal shall be considered if an engineering study finds

that the criteria in either of the following two categories are met (satisfied):

A. If all three of the following conditions exist for the same 1 hour (any four

consecutive 15‐minute periods) of an average day:



Dr. Firas H. Asad

1. The total stopped time delay experienced أتي ‐by the traffic on one minor المت

street approach (one direction only) controlled by a STOP sign equals or

exceeds:

4 vehicle‐hours for a one‐lane approach or 5 vehicle‐hours for a two‐lane

approach; and

2. The volume on the same minor‐street approach (one direction only) equals

or exceeds 100 vehicles per hour for one moving lane of traffic or 150

vehicles per hour for two moving lanes; and

3. The total entering volume serviced during the hour equals or exceeds 650

vehicles per hour for intersections with three approaches or 800 vehicles per

hour for intersections with four or more approaches.

B. The plotted point representing the vehicles per hour on the major street (total of

both approaches) and the corresponding vehicles per hour on the higher‐volume

minor‐street approach (one direction only) for 1 hour (any four consecutive 15‐

minute periods) of an average day falls above the applicable curve in Figure 3 for

the existing combination of approach lanes.



Dr. Firas H. Asad

Finally, if the posted speed limit or the 85th‐percentile speed on the major street

exceeds 40 mph, or if the intersection lies within the built‐up area of an isolated

community having a population of less than 10,000, Figure 3B may be used in place

of Figure 3A to evaluate the criteria in the second category of the Standard.

Warrant 4 ‐ Minimum Pedestrian Volume

This warrant is satisfied when the pedestrian volume crossing the major street on an

average day is at least 100 for each of any four hours or 190 or higher during any

one hour and there are fewer than 60 gaps/hr that are acceptable by pedestrians for

crossing.

The Pedestrian Volume signal warrant shall not be applied at locations where the

distance to the nearest traffic control signal or STOP sign controlling the street that

pedestrians desire to cross is less than 300 feet, unless the proposed المقترحة traffic

control signal will not restrict د تقي the progressive movement ة ة التتابعي الحرك of traffic.



Dr. Firas H. Asad

When this warrant is used, the signal should be of the traffic‐actuated type with

push-buttons for pedestrian crossing.

Warrant 5 ‐ School Crossing

This warrant is used when the main reason for installing a traffic signal control is to

accommodate واء the crossing of the major street by schoolchildren (elementary الحت

through high school students). 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 inadequate for safe crossing of the street by schoolchildren, this warrant is

applied. The standard for satisfying this warrant is that if during the period when

schoolchildren are using the crossing, the number of acceptable gaps is less than the

number of minutes in that period and there are at least 20 students during the

highest crossing hour, the use of traffic signals is warranted. In addition, the nearest

traffic signal along the major street should be located more than 300 ft away or

within 300 ft but the proposed traffic signal will not restrict the progressive

movement of traffic.

The signal in this case should be pedestrian actuated السابلة طةبواس تشغل .

Warrant 6 ‐ Coordinated Signal System

Progressive movement in a coordinated signal system sometimes justifies

(necessitates) installing traffic control signals at intersections where they would not

otherwise be needed in order to maintain proper platooning طابور of vehicles. For

example, when adjacent traffic‐signal controls are at long distances from each other,

the result is unfavorable platooning.

This warrant justifies the installation of traffic lights when 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 1000 ft.



Dr. Firas H. Asad

Warrant 7 ‐ Crash Experience

This warrant is used when the purpose of installing a traffic signal control is to

reduce the number and severity of crashes at the intersection. The need for a traffic

control signal shall be considered if an engineering study finds that all of the

following criteria are met:

1. Crash frequency has not been reduced by an adequate trial اوالت مح of less

restrictive measures عالجات اقل حدة.

2. Five or more injury or reportable property‐damage‐only crashes ات حوادث اضرار الممتلك

ط فق have occurred within a 12‐month period and that signal control is a suitable

countermeasure عالج for these crashes.

3. The traffic and pedestrian volumes should not be less than 80 percent of the

requirements specified in the minimum vehicular volume warrant (see Table 1

Condition A), the interruption ة اعاق of continuous traffic warrant (see Table 1

Condition B), or the minimum pedestrian volume warrant.

Warrant 8 ‐ Roadway Network

This warrant justifies the installation of signals at some intersections when such an

installation will help to encourage concentration and organization of traffic

networks. The need for a traffic control signal shall be considered if an engineering

study finds that the intersection of two or more major routes meets one or both of

the following criteria:

1. The total existing or immediately projected ي ن االن المخم entering volume is at least

1000 during the peak hour of a typical weekday and,

The five‐year projected traffic volumes, based on an engineering study, satisfy the

requirements of the following warrants: Warrant 1 (eight‐hour vehicular volume),

Warrant 2 (four‐hour vehicular volume), or Warrant 3 (peak‐hour volume) during an

average weekday.



Dr. Firas H. Asad

2. The intersection has a total existing or immediately projected entering volume of

at least 1,000 vehicles per hour for each of any 5 hours of a non‐normal business

day (for USA, Saturday or Sunday).

A major route ار الرئيسي considered for this warrant should possess at المس least one of

the following characteristics:

• It is a component of a street or highway system that serves as the principal

roadway network for through traffic flow.

• It is a component of a street or highway system that includes rural or suburban

highways outside, entering, or traversing a city.

• It is designated as a major route on an official transportation plan or equivalent

standard plots.



Dr. Firas H. Asad

Documents

Lec 03 Intersection Control