SmartSensor Matrix is part of a stop bar detection system at Utah intersections that gives green lights not just to drivers but also to bicyclists stopped at red lights.

Project Team

Utah Department of Transportation

Project Scope

The Utah Department of Transportation is using SmartSensor Matrix’s unique true presence detection capabilities to give green lights to bicycles detected at the intersection stop bar. The system is in response to proposed legislation that makes it legal for Utah bicyclists to ride through red lights if they have waited at the intersection for at least 90 seconds. The law passed in 2013, despite objections from transportation officials who argued that it puts bicyclists at increased risk. The Matrix system was implemented at nine Salt Lake City intersections to show that there are safe ways to give bicyclists the green light.

Problems and Challenges

Traditional stop bar detection methods do not always detect bicycles. Unless bicyclists have a car in their lane to trigger the light for them, they could wait undetected for a long period of time before the light turns green. As a result, bicyclists often choose to run the red light, a choice many officials say can be deadly.


UDOT’s simple system uses SmartSensor Matrix and a bike decal painted on the road. The decal lets cyclists know exactly where they need to stop in order to be detected by the sensor. When a cyclist stops on the decal, he falls within one of Matrix’s programmed zones and is detected just as any vehicle would be. If traffic is light on the cross street, then the bicyclist is given the green light. While a cyclist cannot completely stop rush hour traffic, he will get the green light much more quickly, because he will not be forced to wait at a red light when there is little or no cross-traffic demand.


The simple Matrix system deployed by UDOT has proven to be both cost-effective and safe. To save money, UDOT focused on intersections along main cycling corridors with high traffic cross streets at which Matrix units were already deployed. Safety for cyclists has increased because the innovative system helps cars and bicycles share the road; cyclist wait times at red lights have been significantly reduced, so fewer cyclists are choosing to run the red light. Based on the success of this system, UDOT hopes to deploy similar systems at other Matrix intersections statewide.

For more information on SmartSensor Matrix, click here.