Intersection conflict & trail warning systems

Intersection conflict and trail conflict warning systems are traffic control devices that provide road users with a real-time, dynamic warning of vehicles or pedestrians that are approaching or waiting to enter an intersection or crossing.

Key characteristics




WSDOT regions

Strategy description

Intersection conflict and trail conflict warning systems provide real-time, dynamic alerts to the traveling public about vehicles or pedestrians that are approaching or waiting at intersections or trail crossings. These traffic control devices improve awareness of others and help reduce collisions and increase intersection safety.

In the United States, an average of one-quarter of traffic fatalities and roughly half of all traffic injuries involve intersections. Transportation agencies use dynamic intersection conflict warning systems and trail crossing conflict warning systems to reduce collisions at intersections and trail crossings.

These systems use detectors, roadway signs, and flashing lights to alert motorists of potential intersection conflicts. For example, an agency can install video cameras to detect vehicles stopped at a minor road stop sign. When the system sees a vehicle stopped at the intersection, it triggers flashing lights on top of a yellow sign on the major road that reads, “Vehicle Entering When Flashing,” to tell nearby drivers that vehicles might be pulling out.

The system can also work the other way to give more information to drivers on minor roads or people crossing from a trail. The system can detect vehicles approaching on the major road, triggering signs on the minor road or trail to alert road users with one of these messages:

  • Traffic Approaching When Flashing
  • Look For Traffic
  • A visual graphic display of the intersection that indicates which direction a major road vehicle is coming from

The warning information provides road users with improved awareness of others at or near the intersection or trail crossing.

When to use this strategy

Intersection conflict and trail warning systems make sense for unsignalized intersections and trail crossings with risk factors like a history of intersection collisions, high volumes on one or all of the intersection legs, sight distance restrictions, or other evidence of safety conflicts discovered in the field.

Strategy benefits:

  • Helps to reduce the number of collisions and their severity. A recent Federal Highway Administration (FHWA) research study calculated a 20% reduction in collisions at rural stop-controlled intersections.
  • It can address multiple types of travelers approaching an intersection, increasing awareness and safety for vehicles, bicycles, and pedestrians.

What you need in order to implement

Policy needs:

  • Agencies can develop policies to standardize implementation of intersection conflict and trail conflict warning systems, including communication tools, approved products, and desired messaging on the signs.

Planning needs:

  • Intersection conflict and trail conflict warning systems can often be installed without environmental or right-of-way impacts. In some cases, the cost is low enough to be completed within operating budgets.

Coordination needs:

  • Normal coordination will be required with utilities.

Equipment needs:

  • Detection equipment that could include loop detectors, video cameras, or radar.
  • Communications from the detectors to the signs, either wired or wireless, would also be needed.
  • Sign installation equipment that includes power supply (typically hard line to an existing electrical pole or solar power installation).

Maintenance Needs:

  • As a supplemental safety device, it is very important for the system to be tested regularly to ensure that it is operational. Signs should be maintained on a regular schedule.

Agency resources needs:

  • Traffic engineers should place the signs, identify the appropriate messaging, and calculate sight distances to set proper system values.

Learn more about this strategy

Federal Highway Administration (FHWA) Stop-Controlled Intersection Safety: Through Route Activated Warning Systems, Washington, DC. 2011 (PDF).

Minnesota DOT Research Services / University of Wisconsin-Madison. Best Practices Synthesis and Guidance in At-Grade Trail-Crossing Treatments (PDF). 

Federal Highway Administration (FHWA) Safety of Intersection Conflict Warning Systems.

University of Minnesota Center for Transportation Studies, Rural ICWS Evaluation and Design Investigation: Final Report

Enterprise Pooled Fund, ICWS Informational Booklet (PDF).

Works cited:

(1) FHWA Office of Safety, Intersection Safety web page.

(2) FHWA Safety Evaluation of Conflict Warning Systems.

About key characteristics

Location notes:

Though not disallowed in urban settings, intersection conflict and trail conflict warning systems work well at rural, unsignalized intersections.

Cost notes:

Some costs will be incurred to purchase and maintain the equipment. However, most costs will be upfront.

Technology notes:

Detection technologies like video cameras and radar sensors are necessary for the agency to identify when vehicles approach the intersections. Wired or wireless communications technology devices provide a signal from the system to activate nearby warning signs.

Collaboration notes:

The agency responsible for the road can identify the need and implement this solution. Normal coordination will be required with utilities, and in rare cases, with adjacent property owners if right-of-way acquisition is needed.