The Ada County Highway District (ACHD) is looking at “smarter signal” adaptive technology that would automatically detect oncoming cars and intelligently adjust the timing of traffic signals accordingly. Theoretically the new system should be more responsive to waiting traffic and reduce driver delay.
Terry Little, traffic services manager for ACHD, said an adaptive traffic control system will pick up data from the intersection where it’s installed and also from other sets of traffic lights, camerasand detectors placed earlier up the road. Using the information, the system will then adjust the signal cycle length continually, improving efficiency and traffic flow.
The change will be a significant upgrade for the area. Currently Ada County operates two types of traffic signals. One is a fixed-time system used in downtown areas, which sets traffic signals to change at preset intervals based on the time of day. The other is an actuated response system, which runs off detectors embedded in the pavement or cameras — setting a particular cycle length depending on what time it is and the traffic flow it observes.
An adaptive traffic system such as the one planned for Ada is a natural progression from existing actuated systems. The adaptive system’s distinguishes itself by adjusting signal lengths according to more data sources.
Little said 99 percent of the traffic signals in the U.S. are either fixed or actuated. Although adaptive technology has been used in Australia and England for decades, it’s only now getting to the point where all the bugs have been worked out.
He called older versions of the adaptive signal technology a “black box” where little could be done to adjust the system. Signal engineers did not have the ability to tweak the parameters of the adaptive traffic control systems if they weren’t working correctly, so it was more of a crapshoot on whether the investment would be worth the money and effort to get it online.
“It’s been an all-or-nothing thing,” Little explained. “You can’t turn the switch on and go to adaptive, find out that it doesn’t work and go back to your traditional actuated, normal-time-of-day operation. You put yourself out on a limb.”
That has changed, however. Little added he’s been interested in bringing the technology to Ada County since 2004, but waited until now to make sure there was enough variety in the marketplace. The ability to shut off adaptive control is one of the features the county will place a high priority on when deciding which system to select.
Project Details
Not every intersection in Ada County will be upgraded. Initially 20 to 30 traffic lights will be equipped with adaptive traffic control systems in a first deployment. The first phase will cost approximately $600,000.ACHD will pay for the project using federal funds initially earmarked for a bridge the county decided not to build. Instead, adaptive traffic control will be bought to improve alternate routes near the site.
ACHD will be selecting a system in the next year, with plans to roll it out in 2013.
So how will the technology be evaluated? Little said a reduction in driver complaints would be a good first step, but from a technical standpoint, it’ll be a hybrid of measuring travel times in a reduction in traffic delays.
It won’t be easy, however.
“One of the difficult things over the years in assessing whether these things are working or not is that it’s difficult to get a handle on what your total delay is,” Little said. “You have cars backed up on side streets — along the routes — so to measure how many cars are waiting and how long has always been a horrendous obstacle. [But] we’re getting to a point where more systemized technology can help us bring that data in.”
