University of Minnesota study on how to get more cars through green lights shows promise

Traffic signals are not always smart enough to stay green when lots of vehicles are trying to pass through an intersection, but they might be in the future.

Researchers with the University of Minnesota's Center for Transportation Studies have been testing a new method for signal timing in which an algorithm measures traffic volumes at an intersection in real time and tells the controller which direction to grant a green light.

In laboratory testing, the system — called max-pressure signal timing — has been found to significantly improve traffic flow by allowing more vehicles through a single green light, said researcher Michael Levin, an assistant professor in the U's civil, environmental and geo-engineering department.

"Large reductions in delay suggest that this new method of signal timing could achieve higher throughput during peak demand and be more responsive to queues," he said.

Max-pressure uses a sensor embedded in the pavement to count the number of vehicles waiting at the intersection. A second sensor counts the number of vehicles approaching the intersection. The algorithm can determine how long a light needs to stay green to get most of them through.

The algorithm can recalculate every few seconds, and adjust a signal's phase based on the conditions, Levin said.

Levin and his team took data from Hennepin County and used the max-pressure algorithm to model traffic flow at seven intersections on County Road 30 and County Road 109/85th Avenue. They found large reductions in delays — as much as 50% — that drivers incurred sitting at red lights.

While the results suggest a "high potential for use in Minnesota," as Levin wrote in a December 2022 report, don't look for max-pressure at an intersection any time soon.

The algorithm, originally devised in 2013 at the University of California, Berkeley, has advanced to experimental testing on roads in India, Indonesia and Israel, but more study needs to be done before that happens here, Levin said.

"We took the Berkeley mode and tweaked it, and added a few things to make it more practical," he said.

In its original version, the max-pressure algorithm didn't include maximum wait times, meaning drivers and pedestrians on less-traveled roads could be left waiting long periods before getting permission to cross. That has been modified, but other issues remain, Levin said.

Next steps include testing max-pressure with Hennepin County's current traffic signal equipment and determining what software might be needed to deploy it. Once that is figured out, there is a possibility of a pilot project, Levin said.