Speed-sensitive traffic lights show promise in slowing drivers and reducing crashes

Traffic signals that reward drivers for staying within the speed limit are showing encouraging results in several US cities. The systems keep lights red by default, then provide an earlier green to vehicles approaching at or below the posted limit.

Albuquerque, New Mexico, uses the approach on Lead and Coal avenues, parallel one-way streets through residential areas. City officials credit it, alongside nearby speed cameras, with a substantial decline in crashes and injuries. A resident of the corridor also reports hearing far less late-night racing since the signals were introduced.

Portland, Oregon, recently began using similar technology overnight on Southeast Powell Boulevard. At the first intersection tested, the average vehicle speed fell from 39 mph, or 63 kph, to the 30 mph, or 48 kph, limit. Oregon State University researchers are now evaluating the system, including whether it could have unintended effects such as increased red-light running.

The broader “rest in red” concept also has supporting evidence beyond these sensor-based trials. A 2023 study of five roads in North Carolina found a 43% reduction in total crashes after signals were programmed to remain red until vehicles approached. Researchers caution that more evidence is needed before drawing broad conclusions, but the early findings suggest traffic lights can shape safer behavior without physically rebuilding a road.