Traffic Signal Warrants
Traffic signals are valuable devices for the control of vehicle and pedestrian traffic. However, because they assign the right-of-way to the various traffic movements, signals exert a profound influence on traffic flow. Properly located and operated control signals may provide for the orderly movement of traffic, increase the traffic-handling capacity of an intersection, and reduce the frequency of certain types of accidents. After extensive study and analysis, the Federal Highway Administration developed the 8 traffic signal warrants contained within the Manual On Uniform Traffic Control Devices (MUTCD).
Eight Warrants from the Manual On Uniform Traffic Control Devices.
These 8 warrants define minimum conditions under which signal installations may be justified. The Manual suggests that traffic control signals should not be installed unless one or more of the signal warrants are met. However, the satisfaction of a warrant or warrants is not in itself justification for a signal. Every situation is unique and warrant guidelines must be supplemented by the effects of specific site conditions and the application of good engineering judgment. Installation of a traffic signal should improve the overall safety and/or operation of an intersection and should be considered only when deemed necessary by careful traffic analysis and after less restrictive solutions have been attempted.
Warrant 1 - Eight-hour vehicular volume - at a location where a large volume of intersecting traffic exist for each of any 8 hours of an average day, is the principal reason to consider installing a traffic control signal.
Warrant 2 - Four-hour vehicular volume - at a location where traffic conditions are such that for a minimum of 1 hour of an average day, the minor street suffers undue delay when entering a major street.
Warrant 3 - Peak hour vehicular volume - at a location where traffic conditions are such that for a minimum of 1 hour of an average day, the minor street traffic suffers undue delay when entering or crossing the major street.
Warrant 4 - Pedestrian volume - at a location where the traffic volume on a major street is so heavy that pedestrians experience excessive delay in crossing the major street.
Warrant 5 - School crossing - at a location where school children cross the major street, is the principal reason to consider installing a traffic control signal.
Warrant 6 - Coordinated signal system - progressive movement in a coordinated signal system sometimes necessitates installing traffic control signals at intersections where they would not otherwise be needed in order to maintain proper platooning of vehicles.
Warrant 7 - Crash experience - at location where the severity and frequency of crashes are the principal reasons to consider installing a traffic signal.
Warrant 8 - Roadway network - at location where it might be justified to encourage concentration and organization of traffic flow on a roadway network.
Listed below are general characteristics of traffic signals:
Traffic control signals that are properly located, operated and maintained may have one or more of the following advantages:
- Signals may provide for the orderly movement of traffic by assigning right-of-way to conflicting movements of traffic.
- Signals may increase the traffic-handling capacity of an intersection by permitting conflicting streams of traffic to share the same intersection.
- Signals may reduce the frequency of certain types of accidents, especially right-angle (broadside) collisions.
- Signals may provide for continuous movement and progression of traffic through coordination with surrounding traffic signals.
- Signals may interrupt heavy traffic to allow both vehicular and pedestrian traffic to cross.
Traffic control signals may have one or more of the following disadvantages:
- Signals may increase delay - both overall intersection delay and/or specific movement delay.
- Signals may encourage the use of alternate and/or less adequate routes by drivers wishing to avoid the signal.
- Signals may encourage increased volumes of traffic on the minor street by drivers wishing to use the signal.
- Signals may encourage disobedience and disregard of traffic control devices. (During periods of lesser volume on the main street, drivers on the minor street may have sufficient gaps to cross and/or enter traffic, but be prohibited from doing so by the signal.)
- Signals may cause an increase in the frequency of certain types of accidents, especially rear-end collisions.