City officials are experimenting with a network of artificial intelligence-equipped traffic signals to manage congestion on Franklin Street, one of the city’s busiest thoroughfares.

Crews are equipping signals at 10 intersections between Commercial Street and Marginal Way with sensors that are designed to track and respond to traffic in real-time, instead of having the signals change based on a predetermined timing. Outdated, poorly coordinated signals may contribute to rush-hour congestion that bedevils the street, especially in the north end, near the on-ramp to Interstate 295 and Marginal Way.

“I know how frustrated people are with Marginal and Franklin and I don’t disagree with them,” City Manager Jon Jennings said in an interview.

About 27,000 vehicles travel on Franklin Street around Marginal Way daily, city staff said.

Maine Department of Transportation this year proposed a $5.4 million redesign of the I-295 interchange to alleviate congestion and improve traffic flow. But city councilors voted in February to delay the plan because of the $4.3 million cost to the city.

Instead, they sought less expensive options. For Jennings, that meant deploying the same artificial-intelligence units the city installed on signals on Forest Avenue last year. Those upgrades have eased traffic jams and reduced travel time by 23 percent, and similar technology installed near the Casco Bay Bridge on-ramp eased backups on Commercial Street, Jennings said. He hopes for the same result on Franklin Street, at a lower cost – about $775,000.

“Instead of letting a bad situation continue, what I was hoping to do was experiment with technology,” Jennings said. “It is an opportunity to really look at this technology and see if it is really effective.”

The Maine Department of Transportation supports towns and cities that want to explore adaptive signals, also called smart signals, as an option, and is considering equipping four Franklin Street intersections with modern signals to help traffic flow. In a report last year, the department recommended replacing all of the state’s outdated traffic signals and installing up to 30 adaptive signals in certain intersections statewide.

But technology alone may not fix the problem at Franklin Street, and construction to improve the poorly designed interchange with I-295 still might be needed, especially if congestion there creates safety problems for the highway, department spokesman Paul Merrill said. The crowded interstate has a recent history of frequent vehicle crashes.

“We are always willing to work with the city of Portland to improve mobility and safety with people getting in and out of the city using state roads,” Merrill said. “If traffic increases enough, signal upgrades are not going to be the be-all, end-all of fixing any issues there.”

Traditional traffic signals are timed to switch based on observed traffic flows at different times of the day. But that method does not always work in variable and unpredictable traffic, and outdated signals can be mistimed. Bad signals can account for more than 10 percent of all traffic delays and congestion on major roadways, the Federal Highway Administration says.

Adaptive signals, on the other hand, have sensors that allow them to assess traffic flows in real time and adjust signal length and timing to improve the flow of vehicles. Most of the new equipment on Franklin Street will have advanced sensors that can detect traffic coming from hundreds of feet away.

“Essentially it is putting a brain in every traffic signal on Franklin,” Jennings said. “Operationally, that brain is learning the traffic movements, the time of day, all the relevant data that goes into the operational timing of the signals.”

The upgrades are being installed this week. It could take up to a month for the equipment to learn and respond to local traffic patterns.

There is no guarantee that technology holds the solution to Franklin Street traffic, but Jennings is willing to experiment to see what can be accomplished. If it doesn’t work, the technology can be shifted to different intersections that might respond better, he said.

“What we have all over the city is very old traffic signals that have not been replaced in a very long time,” Jennings said. “Unfortunately it is something the city has not invested in over the years.”

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