Inside Boston City Hall, behind a nondescript door on the seventh floor, is a relatively small room. Walk in and you see a standard meeting table in front of you and a few small offices to the right.
Past the table and what comes into view looks a lot like a small television control room. It is not particularly modern or elaborate but there are dozens of camera feeds on some 10 wide screen TVs.
This is Boston's Traffic Management Center, the nerve center for the city's entire network of traffic signals.
There are almost 900 traffic signals in the city, according to Keith Bynum, Senior Traffic Engineer in the Boston Transportation Department Signals Division. And he says each is given a lengthy survey every five years when they are monitored for hours at a time to generate a number of data points.
"There's actually a lot involved," he said of these surveys. "[We note] all the characteristics of the intersection: how many lanes, turning movement counts, the heavy truck movements, parking/blocking maneuvers."
The data is fed into a software program, which helps engineers determine each signal’s optimal cycle length. Essentially, how long should it be green and how long is should it be red?
Most of the city’s signals — about 70 percent — are not just statically timed with the help of computers, they are also coordinated and controlled by them according to a recent report from the Boston Traffic Management Center.
"So, we have central computer control over those signals," explained Bynum.
The system runs on an automated schedule. And for the 699 signals on it, there isn’t just one set cycle length. Traffic ebbs and flows through the day. So there are four separate default modes, called "time of day patterns," each timed a little differently.
There are a.m., off-peak, p.m. and overnight — when many of the signals go from a stop-go pattern to blinking — settings. But the real work — for traffic engineers like Bynum — is a little more artisan.
"The computer’s not perfect," said Bynum. "That’s why we have to adjust and optimize it for real life conditions out there."
By "optimize," Bynum meant engineers step in and make changes in real time. Engineers operate some 300-plus cameras on traffic signals and have access to another 500 or so operated by the police department and MASSdot to monitor traffic conditions across the city - .
The city’s signals are grouped geographically — essentially by neighborhood — so engineers can step in and target specific problem areas with the touch of a few buttons.
Bynum cited the example of a Saturday, when the city would typically be in an off-peak pattern.
"And there’s something going on at the Garden, so traffic Is heavy around Faneuil Hall and the Garden. I can just put that area into the PM pattern that I run on weekdays which usually has a higher cycle length to manage more traffic."
During weekday morning and evening rush hours, two to three engineers monitor hundreds of individual traffic signals — tweaking the timing to keep things moving as best as they can.
"It doesn’t take a lot of green time to actually improve traffic over five to ten minutes," said Bynum. "So two, three, four, five seconds can make a big difference."
Still, there are limits to what they can do.
When there is enough traffic on the roadways, something Bynum called "exceeding capacity," it is a challenging to keep traffic moving in both directions, especially at the intersection of two busy streets.
Adding time to a green light for means your have to add red time to the other. Case in point, the intersection of Atlantic Avenue and Seaport Boulevard near an entrance ramp to 93 North — a notorious trouble spot at rush hour.
"We’ll take time away from Seaport, so that will cause Seaport to back up," said Bynum. "But [those cars] have nowhere to go...when traffic backs up from the ramp toward the intersection. But Atlantic Avenue, if it keeps backing up, it will effect Congress Street, it will effect Summer Street, it will effect Esssex Street, it will effect Kneeland Street."
In essence, because Atlantic Avenue would affect more streets, that green light gets more time compared to Seaport Boulevard.
Boston’s unique layout is not a grid and that just complicates matters.
And plenty of signals are managing more than just two cross streets.
"Instead of just two streets it’s three streets or four streets," said Bynum. "Like Andrew Square or Arlington, Columbus, and Stewart."
Signals in busy pedestrian areas include what is called a pedestrian recall — a walk sign built automatically into every cycle.
To complicate matters further, it is not uncommon for signals to go off-line as many of them are hard wired and can be disrupted by anything from a bad connection to damage due to construction or street maintenance.
"The signal will still work out in the field, but it’s no longer in communication with our system," said Bynum. "It’s basically running free, out of sync with the rest of the signals in that corridor."
The City does plan to experiment with the system over the coming years as they roll out 47 signals in the Seaport neighborhood over the coming years to monitor traffic, "talk" to each other in real-time, and adjust on the fly — fully automated.
Bynum said he is excited for it and hope it works. Even if it could, eventually, put engineers like him out of a job.
