How Traffic Signals Are Warranted

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 while reducing the overall capacity of the roadway on which it is placed and reduce the frequency of certain types of accidents. After extensive study and analysis, the Federal Highway Administration developed the 11 traffic signal warrants contained within the Manual On Uniform Traffic Control Devices (MUTCD).

11 Traffic Signal Warrants

These 11 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. The 11 warrants are:

• Warrant 1 - Minimum vehicular volume: Traffic volumes on intersecting streets exceed specified values for any 8 hours on an average day.
• Warrant 2 - Interruption of continuous traffic: The traffic volume on a major street is so heavy that traffic on a minor intersecting street suffers excessive delay or hazard in entering or crossing the major street. Specified values are exceeded for any 8 hours on an average day.
• Warrant 3 - Minimum pedestrian volume: The vehicular volumes on a major street and the pedestrian volumes crossing that street exceed specified values for any 8 hours on an average day.
• Warrant 4 - School crossing: Inadequate gaps exist in traffic for schoolchildren to cross at established school crossings.
• Warrant 5 - Progressive movement: Signalization is necessary to maintain proper grouping or platooning of vehicles and effectively regulate group speed.
• Warrant 6 - Accident experience: The number of reported accidents potentially preventable by a signal exceeds a specified value. Additionally, volume requirements of warrants 1, 2 or 3 are 80% satisfied and less restrictive solutions have been attempted.
• Warrant 7 - Systems: This warrant encourages concentration and organization of traffic flow networks.
• Warrant 8 - Combination of warrants: No single warrant is satisfied, but warrants 1 and 2 are satisfied to the extent of 80% or more.
• Warrant 9 - Four Hour Volumes: In each of any four hours of an average day, the hourly volumes on the major street and the minor street exceed specified values.
• Warrant 10 - Peak Hour Delay: For one hour of an average day, the minor street traffic suffers undue delay in entering or crossing the major street.
• Warrant 11 - Peak Hour Volume: The peak hourly volumes on the major street and the minor street exceed specified values for any one hour of an average day.