In an ideal world, traffic signals would instantly know when to give a longer green light to vehicles that need it most.
Is an accident clogging a nearby intersection? They’d know. Is a broken-down vehicle wreaking havoc ahead? They’d know that, too.
Montgomery County soon will begin evaluating whether such “adaptive signal control” technology that adjusts traffic light timing to real-time conditions would make enough of a difference — saving travel time, cutting vehicle emissions, making trips more reliable — to be worth the cost.
The $480,000 study, expected to begin in July and take 15 months, also will examine where the signals would make the most difference. Arlington County is believed to be the only other Washington-area jurisdiction with a similar system.
Montgomery County Council member Roger Berliner (D-Potomac-Bethesda), who pushed for the evaluation funding, said studies have found such better-timed signals can cut travel times by
“That’s good for our citizens and good for our environment and good for our quality of life,” Berliner said. “So, what’s not to like about this?”
But traffic engineers say that while such technology has become more affordable, it still is a significant investment. The sensors embedded in asphalt and managed by computer software can cost between $6,000 and $50,000 per intersection, depending on the technology used, according to a consulting firm’s report for the county. Montgomery County has about 800 signalized intersections.
Emil Wolanin, chief of traffic engineering and operations for the county, said such signals have been around since the 1970s, but costs have limited them to about 5 percent of U.S. jurisdictions. He said he has heard of some systems being abandoned after they became too expensive to maintain and replace.
“We want to see if this is a good fit for Montgomery County,” Wolanin said. “Would we get 15 percent improvement [in travel times] from this? It’s hard to say.”
Larry Marcus, Arlington’s head of transportation engineering and operations, said the county began using adaptive traffic signals 10 years ago on Arlington Boulevard (Route 50), Lee Highway (U.S. 29) and Columbia Pike. Travel-time savings are difficult to quantify because they vary so much daily, Marcus said, but each signal is believed to save an average 8,395 gallons of fuel annually. The signals also provide information to message signs that tell motorists how long a trip will take in current traffic conditions.
“They keep traffic moving, they’re efficient from a
cost-savings perspective, and they’re quite beneficial to the public because of the information they get about expected travel times,” Marcus said.
Wolanin said Montgomery County now presets signal times based on peak traffic flows at different times of day and other considerations, such as the number of pedestrians at particular intersections. If a collision or other incident requires giving traffic in one direction a longer green light, Wolanin said, engineers can manually override a signal’s timing to adjust as needed.
The upside of the adaptive technology, he said, is that such signal-timing changes would occur automatically and immediately.
Both Berliner and Wolanin said they don’t see implementing such a system countywide. Some particularly busy intersections and roads that must handle more vehicles than they were designed to don’t see much improvement from signal timing, Wolanin said.