Traffic signals adapt to traffic in real time to speed commutes

PHOENIX ‒ Drivers along one of northern Pima County’s busiest roads are now benefiting from a technology that adjusts the timing of traffic signals based on how many vehicles are on the road.

The Arizona Department of Transportation installed an adaptive signal timing system this summer to improve traffic flow on State Route 77 (Oracle Road), the primary north-south route connecting Tucson and Oro Valley. The roadway serves about 60,000 vehicles each day.

The early results are good news for area commuters. Travel times over 8.5 miles between Tangerine Road and Rudasill Road south of Orange Grove Road have been reduced by about 10 percent – about two minutes off the morning southbound commute that used to take as long as 20 minutes.

“Sensors on the corridor provide information about the speed and volume of traffic on the road,” said James Gomes, ADOT traffic engineer in Tucson. “The software uses that data to send information to each traffic signal along the route and adjust the signal timing to accommodate the traffic demand we’re experiencing at the time.”

The system can modify the length of signal cycles, including left turn signals, and can account for changes in traffic volumes and speeds.

Northbound travel times have improved by one minute during the afternoon commute and as much as three minutes earlier in the day.

Engineers also have seen a secondary benefit: Since signals are timed to the speed limit during non-peak hours, more drivers are traveling at the speed limit.

The system, funded by ADOT and the Regional Transportation Authority, is the first of its kind in Pima County. The first such system in southern Arizona was installed along SR 189 in Nogales in 2015.