The Arizona Department of Transportation (ADOT) installed an adaptive signal timing system this past summer in Pima County to improve traffic flow on S.R. 77 (Oracle Road), the primary north-south route connecting Tucson and Oro Valley, which handles about 60,000 vehicles per day.
Thus far, according to ADOT, 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% – 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 signal cycle duration, including the timing of 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. For those who feel this is small potatoes, just ask any traffic engineer if these results are meaningful.
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, which increases safety and reduces the likelihoods of traffic incidents and injuries.
The system, funded by ADOT and the Regional Transportation Authority, is the first such system installerd in Pima County. Previously, a similar system was put in place in 2015 in southern Arizona along S.R. 189 in Nogales.