Freight or truck signal priority

Freight (or truck) signal priority (FSP) provides extra green light time so that a heavy truck can move through a traffic signal without stopping.

Key characteristics

Setting/Location

Corridor, Urban, Suburban, Rural

Technology

Collaboration

WSDOT regions

Other names

  • truck signal priority

Strategy description

Freight (or Truck) Signal Priority (FSP) is a traffic signal modification that extends a green light’s timing to allow an approaching truck to make it through an intersection without stopping. The main purpose for giving trucks extra green time is increase safety by reducing the potential for the truck to run a red light and cause a collision. The secondary purpose is to reduce the delays and congestion that are caused by the longer time it takes trucks to accelerate to the posted speed limit.

With FSP, priority is given to a heavy truck that may be close to the traffic signal and have a hard time stopping when the light turns yellow. This is especially important when the approach to the traffic signal is on a high-speed roadway or on a downhill approach. Priority may also be provided to a truck on an uphill approach, so that they can clear the intersection with a little extra green time in order to reduce delay and congestion.

FSP requires different detection technology than transit signal priority because trucks are operated by private companies, making it impossible to have the same equipment on all trucks. To provide FSP, agencies rely on intersection detection that can identify an approaching truck and determine its speed.

Providing FSP requires the following equipment:

  • Traffic signal controller software with logic to distinguish a truck priority request from a transit priority request and the ability to configure an extended green time
  • Detection equipment that can classify vehicles, identify large trucks, and determine the speed of an approaching truck. Note: the vehicle length is typically used to determine if it’s a truck, and the weight of the truck is not detected.

Unlike transit signal priority, FSP only extends the amount of green light time and does not bring up the green early.

When to use this strategy

FSP makes sense for corridors and routes with traffic signals where:

  • A corridor is an important freight route that is used by a lot of trucks. Important freight routes may be designated truck routes near ports, industrial areas, or distribution centers.
  • The approach to a traffic signal is uphill where the time to accelerate from a red light is longer.
  • The approach to a traffic signal is downhill and trucks may have to brake harder to stop in time for a red light.

Strategy benefits:

  • Improves safety by reducing truck-related collisions at intersections. When trucks are unable to stop after a light turns yellow, they may enter the intersection after the light turns red and cause a serious collision.
  • Reduces congestion by giving extra time to slower-moving vehicles. Trucks stopped at traffic signals contribute to congestion because it takes trucks longer than smaller vehicles to get up to speed when the light turns green. Keeping the trucks moving through a green light reduces traffic delays.
  • Reduces road maintenance needs by limiting stop-and-go conditions. The amount of time trucks stop and start at intersections causes more wear and tear on pavement. Keeping trucks moving helps reduce maintenance costs and labor.
  • Reduces emissions from trucks waiting at red lights and accelerating from a stop at the traffic signal.

What you need in order to implement

Policy needs:

  • Consider creating a freight priority policy and signal timing procedures.

Planning needs:

  • Determine if the traffic signal is on an important freight route and if FSP would improve safety and travel time reliability.
  • Engage the freight industry to coordinate the design and installation of FSP. This is particularly important when short-range radios will be used.

Equipment needs:

Onboard technology to locate the vehicle, assess its status, and communicate the request to the appropriate signal or signal system

Roadside or central technology to receive priority request communications and determine whether to grant the request, as well as signal software to process the request and store the data

Vehicle Detection - Several options exist to help detect that a truck is approaching a traffic signal and will need extra time to clear the intersection.

  • Inductive loops detectors - Loops are embedded in the pavement and alert the traffic signal when truck metal crosses the loop. For FSP, two loops are needed in each lane, approximately 650 to 750 feet in advance of an intersection. The loops calculate the length of the vehicle and its speed, which the traffic signal uses to decide whether the green time should be extended.
  • Radar detectors - Radar detectors work similarly to inductive loops but are mounted on the traffic signal to detect vehicles approaching from as much as 900 feet away. The radar can tell the difference between a truck and a passenger vehicle, as well as measure the speed of the approaching truck. The traffic signal uses this information to decide whether the green time should be extended so an approaching truck can proceed without stopping.
  • Short-range radios - The use of short-range radios for vehicle detection is a new technology that requires a radio at the traffic signal, as well as onboard the truck. The radios use a dedicated frequency (5.9 GHz) to “talk” to one another and communicate that a truck is approaching and requesting a longer green light.
  • Traffic Signal Software - Traffic signal software is located on a computer (called the traffic signal controller) in a roadside cabinet near the traffic signal. The software must have logic built in to receive the message that a truck is approaching and tell the traffic signal to extend the green light.

About key characteristics

Location notes:

Truck signal priority is most appropriate for intersections on major truck routes and where traffic signals are not synchronized.  

Cost notes:

Truck signal priority is most appropriate for intersections on major truck routes and where traffic signals are not synchronized.  

Technology notes:

Minimal technology is needed to provide truck signal priority. It requires detection equipment that can distinguish trucks from other motor vehicles and measure the speed of an approaching truck. It also requires traffic signal software with the logic to extend the green light.  

Collaboration notes:

If short-range radios are used for truck detection, collaboration is required with truck companies in order to install radios on the trucks. If radar or inductive loops are used for truck detection, then no collaboration is needed.

Conditions this strategy addresses