Everybody knows the feeling: stuck in traffic, waiting for the light to change. Waiting for somebody, anybody, to just … start … moving.

Some people in Pittsburgh are trying to do something about that. In fact, Pittsburgh is about to become a laboratory for large-scale “smart signal” technology. The city and PennDOT are spending $30 million to build what they contend will be the largest adaptive traffic signal system in America.

First, they had to determine what they couldn’t do.

“There are very few opportunities to widen roads within Pittsburgh,” says Karina Ricks, director of Pittsburgh’s Department of Mobility and Infrastructure. “That’s a bygone era. Even if we could, that just means we’re using up valuable real estate where we could be building businesses, housing, parkland.”

The solution is to make the traffic signals smarter.

Normal traffic signals are pretty dumb. They work on pre-set timers for the most part. Some are a little smarter and can be changed by pedestrians pushing a button.

The signals coming to Pittsburgh are smarter still.

Using cameras and other sensors, they can “see” what’s going on, and adjust from moment to moment — communicating with other signals down the street.

“If there’s a ‘Doorbuster Sale’ at Target, they can adjust to that traffic,” says Ricks. “Or if it’s move-in at Pitt — all the students come in at 10 a.m. and are hungry at 1 p.m. The adaptive signals can change themselves to optimize what is happening. They can talk to each other to communicate so the next signal can prepare.”

One small slowdown can create backups elsewhere, and for a long time afterward.

“It’s like a snake swallowing a mouse,” says Ricks. “That bulge, that episodic surge, doesn’t clear until you have a corresponding lull. It continues stacking up. People get very frustrated. That surge lasts longer.”

Carnegie Mellon has pioneered a lot of this technology. CMU spinout Rapid Flow Technologies has been collecting data from smart traffic signals in East Liberty for several years with a technology called Surtrac.

“Where you get the real travel time savings is stringing them along in whole corridors,” says Alex Pazuchanics, associate director of planning for the City of Pittsburgh. “We’re calling it the Smart Spines. There are five corridors for the city where we’re putting it in: Fifth and Forbes Downtown through Uptown, West Liberty and Route 51 in the South Hills. Second Avenue through Hazelwood, and Center Avenue through the Hill District.”

The technology is still being perfected. Cars are fairly easy to predict. Pedestrians are not.

“Adaptive signals ‘look’ at what’s happening in the area around them and make a prediction about where the vehicle is trying to go. If you’re in a lane with a ’through’ arrow, it assumes you’re going straight. It does not assume you’re trying to turn right from a left-hand lane.”

Of any pedestrian queuing at a corner, he says, “it’s really hard to guess where that pedestrian is going to go — they might go left, might go right, might just be there checking texts from a friend.”

Much of the city’s planning was already done for last year’s Smart Cities competition. Pittsburgh was a finalist, though Columbus was ultimately selected to win the $50 million grant. Pazuchanics helped lead Pittsburgh’s efforts.

Of the plan’s estimated $30 million cost, most will come from federal and state money. The city’s investment is $7 million, Ricks notes. This system will take about three years to build out.

The Bus Rapid Transit plan to connect Downtown and Oakland will be integrated into the plan.

“Technology advances rapidly, says Pazuchanics. “Our challenge is to future-proof it. We want to skate where the puck is going — make investments where we can be not just leading edge now, but three years to come.”