Signal timing review & optimization

Signal timing review and optimization synchronizes groups of traffic signals so that vehicles on a primary route can travel through multiple traffic signals without stopping. It can also reduce vehicle wait times at individual intersections by adjusting the length of green lights to match demand.

Key characteristics





WSDOT regions

Other names

  • coordinated signal timing
  • traffic signal coordination
  • traffic signal timing and coordination

Strategy description

Synchronizing traffic signals can dramatically reduce congestion, fuel consumption, and travel times, and produce noticeable benefits to the traveling public. Optimizing the local intersection traffic signal timings can reduce delays by providing a green light to the vehicles that need it.

While it is common to synchronize traffic signals to reduce the number of stops vehicles make at red lights on a primary route, agencies may also want to prioritize other modes such as transit, pedestrians, or bicycles. When prioritizing these modes, agencies may choose to optimize the traffic signals to favor transit or bicycle travel speed or reduce the length of time pedestrians have to wait to cross.

The traveling public can benefit from signal timing optimization because they can travel through multiple traffic signals without stopping. Dramatic improvements in congestion can also occur when new optimized timings are implemented on corridors or primary routes that were not previously coordinated. Signal timing optimization reduces delay, travel times, and fuel consumed.

Optimizing traffic signals often produces a high benefit-to-cost ratio. The cost to design, implement, and fine-tune new signal timings is low compared to major construction projects because it only requires some engineering and technician time, and can be completed in a few months.

There are two approaches to synchronizing traffic signals using preprogrammed timing plans:

  • Time-of-Day Schedule - Traffic signals within a group are optimized and operate the same cycle length to reduce the amount of time vehicles wait at a red light. The cycle length (and related timing plan) may change throughout the day (a.m. peak hours vs. noon peak hours vs. p.m. peak hours). The timing plans are programmed to operate during the same time period every day based on a time-of-day schedule.
  • Traffic Responsive - Traffic signals operate pre-designed timing plans that change based on changes in real-time traffic conditions. Traffic responsive systems use field detectors to measure volumes and occupancy (the amount of time vehicles occupy the detector space) and change the timing plans as the traffic increases or decreases. Either a central system for the traffic signals or a master controller in the field gathers the traffic flow information from each intersection and calculates when the signal timing plans should change. 

When to use this strategy

Signal timing review and optimization to coordinate traffic signals make sense for:

  • Both rural or urban locations where traffic signals are closely spaced (less than 0.5 miles apart) and there is a high volume of traffic.
  • For corridors that have volumes greater than 400 vehicles per hour.
  • For crossing corridors that have a high volume of traffic in all directions.
  • For grid networks, like a downtown area, where the traffic signals must work together to help vehicles move through multiple intersections without stopping.
  • For corridors where helping bicyclists or transit vehicles travel through multiple intersections without stopping is desired.
  • Around special event locations where a high number of vehicles, buses, bicyclists, and pedestrians will be entering or leaving the site at similar times.

Signal timing review and optimization for intersection traffic signal timings make sense for:

  • Any stand-alone or coordinated traffic signal in urban or rural locations. Optimizing the detector and phase (each movement at the intersection) timings can reduce delays and improve safety.

Low traffic volume considerations:

Traffic signals with low volumes or no vehicle detection will benefit less from optimizing the timings. With low volumes, delays will typically be short anyway. Without detection, the traffic signal lacks the ability to change the amount of green time given to better match the vehicle demand.

Strategy benefits:

  • Reduces delay caused by time waiting at a red light caused by signal timings that don’t match the demand.
  • Reduces stops, delays, and travel times along a corridor when the traffic signals are coordinated and work together to give multiple green lights to vehicles moving down the corridor.
  • Reduces excess fuel consumption caused by vehicles waiting at red lights.
  • Signal timing review and optimization is very cost effective and often provides benefit-cost ratios of 40:1 or more (1).

What you need in order to implement

Planning needs:

  • Before designing new coordinated signal timings, the agency needs to understand the operating objectives for the geographic area, which could be an isolated intersection, a corridor with a group of intersections, or a grid network of roads like those found in a downtown. For example, is the objective to reduce travel times on the primary route or reduce the amount of time pedestrians have to wait to cross?
  • The optimized signal timing designer needs to know the number of vehicles, pedestrians, and bicyclists using each intersection
  • To design optimized traffic signals timings, the designer uses a software program to plan the relationship between traffic signals within the selected group

Equipment needs:

  • Vehicle sensors that measure the traffic conditions, and detect pedestrians, bicyclists, buses, and emergency vehicles
  • Intersection traffic signal controller that runs the traffic signal timings
  • Master traffic signal controller (optional) that communicates with each intersection traffic signal controller. The master traffic signal controller sets the current time-of-day and tells the intersection traffic signal controllers what optimized plan to run. One master traffic signal controller is needed for each group of optimized intersections.
  • Central signal system software that monitors the status of each intersection traffic signal and can upload/download new optimized traffic signal timings
  • Communications equipment between each intersection so the traffic signals can talk to the master traffic signal controller or central signal system

Maintenance needs:

  • Optimized traffic signal timings must be updated for a variety of reasons including when traffic conditions change, construction modifies an intersection layout, policies or signal timing standards change, or temporary construction affects the intersection.

Engineering resources and technical skills needs:

  • Optimizing traffic signal timings typically requires an engineer using a software program to design the new optimized signal timings including the cycle lengths, splits, and offsets.

Learn more about this strategy

Federal Highways Administration (FHWA), Traffic Signal Timing Manual, 1st Edition.

Federal Highways Administration (FHWA), Traffic Signal Timing Manual, 2nd Edition (Fee).

Federal Highways Administration (FHWA), Transportation Systems Management and Operations Benefit-Cost Analysis Compendium

Federal Highways Administration (FHWA), Arterial Management Program, Traffic Signal Timing and Operations Strategies.

National Association of City Transportation Officials (NACTO), Urban Street Design Guide, Coordinated Signal Timing.

Works cited:

(1) Federal Highways Administration (FHWA), Traffic Signal Timing Manual, 2nd Edition.

About key characteristics

Location notes:

The use of signal timing review and optimization works best for locations where traffic signals are closely spaced and there is a high volume of traffic.

Cost notes:

Signal timing review and optimization represents one of the most cost-effective ways to reduce travel times on arterial roadways.

Technology notes:

While signal timing review and optimization can work for traffic signals that do not have communications or traffic detection, the optimization benefits from having both. Communications between the individual traffic signal and central traffic signal system allow the engineers and technicians to remotely fine-tune the signal timings.vehicle detection allows the traffic signal controller to allocate more time to vehicles, bicyclists, or pedestrians when needed.

Collaboration notes:

Signal timing review and optimization is typically implemented on corridors or primary routes that are within one agency’s boundaries. In some situations, signal timing optimization is appropriate between traffic signals owned by a neighboring agency and requires collaboration. When optimizing traffic signals between agencies, the time of day must be exactly the same, down to the second, at each traffic signal, which requires a particular method of updating clocks at multiple traffic signals.