Traffic Signal Timing & Operations Strategies
The primary goal of traffic signal timing is to maintain the safe and efficient transfer of right-of-way between complementary and competing traffic demands at intersections. Traffic signal controllers are specialized devices designed to manage the flow of traffic at intersections by distributing capacity in the form of green time to each intersection approach. Signal timing is typically designed, implemented and maintained by the agency with operational authority over the intersection. The responsibility for traffic signal operation and maintenance generally falls to the state, county, city or local agency with jurisdictional authority over the physical location of the intersection; variations to this rule of thumb exists. At a minimum the design and operation of signalized intersection must consider the geometry of the intersection, lane configuration, and location of signal displays, vehicle and pedestrian demands, type and location of detection devices and the configuration of the transportation network.
The Highway Capacity Manual and Manual on Uniform Traffic Control Devices are primary references for professionals that design, implement and maintain traffic signal timing. The FHWA Traffic Signal Timing Manual represents a synthesis of best practice to guide the design, implementation and maintenance of traffic signal timing. Signal timing should be consistent with the operational objectives and policies that satisfy both the local and regional needs of all system users. Agencies responsible for the operation of traffic signals should proactively monitor performance to ensure that operational objectives are being met and are consistent with traffic demands, agency capabilities and resources. The National Traffic Operations Coalition (NTOC) National Traffic Signal Report Card provides a national assessment of how effectively agency programs are supporting the operation and maintenance of traffic signals.
Traffic signal operations strategies can be placed into two broad categories: Isolated or Coordinated. Isolated signal timing is generally designed to minimize delay at the intersections that are not in close proximity to other traffic signals. Coordinated operations strategies promote the smooth flow of traffic between along an arterial to minimize stops, avoid congestion, fuel consumption and air quality impacts resulting from the acceleration and idling of vehicles. Operational strategies consistent with the objectives of coordination include Adaptive Signal Control Technology (ASCT) and Traffic Responsive. The use of Systems Engineering is recommended (required when federal aid funds are used) to address the risks associated with the implementation of ASCT. Guidance and technical assistance is available to assist agencies with the application of Systems Engineering to the implementation of advanced signal operations strategies.