Surtrac, which started as a project at Carnegie Mellon, piloted at 12 high-volume intersections in 2012. It’s now at 50 intersectionswith another 150 on the way, paid for with a grant from the Federal Highway Administration. In 2015, the project spun out from Carnegie Mellon as a company called Rapid Flow Technologies.

After the pilot, Steve Smith, a robotics professor at Carnegie Mellon and the head of Rapid Flow Technologies, said they could notice a significant difference in traffic flow. But they were quickly informed that they had forgotten about non-motorized traffic.

“We immediately got a lot of feedback from pedestrians, who were feeling left out of the picture,” Smith said.

Tweaks to the system made it so there was a maximum wait time for pedestrians at lights. Researchers and students at Carnegie Mellon are working on a side project to make a mobile phone app to communicate with the lights for people with disabilities who need more time to cross the street.