Improving traffic light timing with a handful of connected vehicles

With GPS data from just 6 percent of vehicles on the road, University of Michigan researchers can recalibrate traffic lights to significantly reduce congestion and delays at intersections.

In an 18-month pilot study conducted in Birmingham, Michigan, the team used connected vehicle data provided by General Motors to test its system, resulting in a 20 to 30 percent decrease in the number of stops at signalized intersections. GM vehicles represent 6 to 10% of cars currently on the road in the United States.

Officially, it is the world’s first large-scale, cloud-based traffic light retiming system and represents a major opportunity for communities to recalibrate their traffic light patterns at a reduced cost. UM research appears in Natural communications.

The UM system takes GPS data from a percentage of vehicles on the road and extrapolates traffic patterns. For example, a connected vehicle that stops about 100 feet from an intersection clearly indicates that it is behind at least three or four other vehicles.

“While detectors at intersections can provide traffic counts and speed estimation, access to vehicle trajectory information, even at low penetration rates, provides more valuable data, including vehicle delay , number of stops and route selection,” said Henry Liu, professor of civil engineering at UM. engineering and director of Mcity and the Center for Connected and Automated Transportation.

There are approximately 320,000 traffic signals in the United States, and the annual congestion costs – direct and indirect – associated with these intersections total $22.9 billion. These costs include time spent waiting at traffic lights, as well as unnecessary energy consumption caused by signal times that can be improved.

Most traffic lights operate on a time-of-day light timing plan, in which predefined patterns are in place for morning, afternoon, evening and night. Traffic planners attempt to coordinate these cycles with surrounding intersections to allow cars to travel between intersections with as few stops and starts as possible.

“The reason these signals should be changed more often is because traffic is constantly changing,” Liu said. “A good example is the traffic patterns we saw in the year before COVID hit and the two years since. Your morning rush hour has changed dramatically with so many people working from home. When you see that kind of changes, you have to resynchronize those signals.”

Optimizing signals to track changing traffic flows is no simple task. The costs and time required to count traffic and recalculate mean that most municipalities won’t reassess for two to five years, or sometimes decades.

Although adaptive signals have been around since the 1970s, detecting vehicles at intersections to reprogram signals in near real time, their cost has prevented their widespread use. Installing an adaptive system at a single intersection can cost up to $50,000, with regular maintenance required – a price not all communities can afford. The UM optimization system would cost a fraction of that of an adaptive system.

The UM system, called a probabilistic space-time diagram, allows a smaller percentage of data from connected vehicles to perform the same workload as the sensors in an adaptive traffic light. To test its effectiveness, researchers collected data for three weeks in March 2022 at each of Birmingham’s 34 signalized intersections, most of which are fixed-time systems.

“It really solved our data collection problem,” said Gary Piotrowicz, deputy general manager of the Oakland County Highway Commission. “And I could argue that this will be the way everyone in the country will do it. Once they solidify the system, there will be no reason to do it any other way.”

Liu’s team includes several graduate students, including Zachary Jerome, a graduate research assistant and member of the Michigan Traffic Lab who helped develop the algorithm at UM. Jérôme has worked directly with RCOC and hopes to collaborate with industry partners to help other municipalities deploy this cost-effective technology.

“The opportunity to work with industry to bring this revolutionary technology into real-world applications is incredibly inspiring,” said Jérôme. “My vision is that this system will provide a revolutionary signal resynchronization solution to communities around the world that is scalable, sustainable and efficient.”