Who Taught YOU to Drive?

Real Time traffic and two-tone lights

A motorist snapped this photo on her way to the Cape with her husband and their baby.  She
 was  dismayed to see it would take more than an hour to travel the 17 miles left to the Sagamore Bridge, and wondered if the trip was worth the traffic
Leah Jacob
A motorist snapped this photo on her way to the Cape with her husband and their baby. She was dismayed to see it would take more than an hour to travel the 17 miles left to the Sagamore Bridge, and wondered if the trip was worth the traffic

For the past few years, the MBTA has posted arrival times for trains in subway stations — “Inbound train approaching in 4 minutes,” and so on. But why should strapholders have all the fun?

Drive Greater Boston’s major highways this summer and you’ll notice electronic message boards displaying your trip time in minutes, based on traffic levels, to Exit 28 in Somerville, or the Framingham tolls, or the Interstate 93/95 exchange.

The message boards are part of the Massachusetts Department of Transportation’s “Real Time Traffic Management System,” which debuted on Interstate 93 last year and expanded this May to the Massachusetts Turnpike, Route 6, and Route 3.


Whereas the MBTA’s system is more of a courtesy — once you’ve paid your fare, you’re probably going to wait on the platform whether the next train is 2 or 20 minutes away — the highway boards are supposed to help drivers avoid traffic jams.

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“A board might say 4 miles, 75 minutes. You wouldn’t want to do that. That wouldn’t be a fun trip,” said Sara Lavoie, spokeswoman for MassDOT. “The idea is to let motorists who are on the road know what’s ahead of them so they can make a choice about their route.”

Just how, though, does the system work? How does MassDOT know the number of minutes you are from the posted milestone? Today we answer more of your questions, starting with this one.

Can I borrow your phone?

Westford reader Steve Haber put me onto the subject when he inquired about why roadside cameras had been placed along Interstate 495 near his home. Turns out, they’re tied to the message boards.

Lavoie explained that the state actually has two types of traffic update systems — a permanent one and temporary setups. We’ll cover the permanent one first.


The system in use on Interstate 93, the Mass. Pike, Route 6, and Route 3 relies on detectors — specifically, Bluetooth detectors — to determine updates. When a car passes by one of the detectors, it is scanned for any active Bluetooth devices that might be onboard (let’s say, a cell phone). The system creates a unique identifier for each Bluetooth device that passes, and times how long it takes the device to reach the next detector on the road.

The detectors scan every car that passes by, meaning they record hundreds, possibly thousands, of Bluetooth devices every few minutes. All those data are plugged into an algorithm, which is updated every three minutes to produce an estimated travel time between Point A and Point B. That’s how the “Real Time” system works.

The system Haber noticed is actually a temporary update system used in conjunction with construction-site delays. That system, which the state calls a “Smart Work Zone,” relies on either Bluetooth readings or old-fashioned radar to estimate travel-time delays. MassDOT officials also watch feeds from cameras to monitor both traffic and construction progress, Lavoie said.

The I-495 Smart Work Zone will remain in place until bridge repairs in Westford are completed in August, Lavoie said.

Blink and they’ll be gone

Reader Jeano Morin of Salem posed this question about a subject somewhat dear to me: “Can you please tell me when and why we stopped using red AND yellow traffic lights to indicate pedestrian crossing?”


Once upon a time, drivers knew to stop for people crossing the street when a traffic signal displayed both a yellow and red light. “Walk” signs and illuminated pedestrian symbols eventually were created to handle that duty, and by 1971, combination lights were dropped by the federal government as an acceptable traffic-control device.

Still, a few dinosaurs remained, legally grandfathered in. In 2007 I tracked some of them down — a double light on Charles Street near Beacon Hill, another on L Street in South Boston — and had some fun asking passersby whether they knew what the double lights meant. (Few did.)

Morin’s question got me wondering how many combination lights are left today. Back in 2007, state highway officials told me there weren’t any on state-owned highways. The Boston Transportation Department told me that just nine of 750 city-owned intersections had double lights; the state Department of Conservation and Recreation said it had a few double lights on parkways it maintained.

Boston has since done away with all its double lights, officials said, including the ones on Charles Street. The DCR continues to phase them out as roadways are rebuilt or reconfigured, or when the combo lights break beyond repair, said Bill Hickey, acting press secretary. But they’re not all gone.

“There are a couple of the combo lights on Morrissey Boulevard, as well as West Roxbury Parkway,” he said. Catch them while you can.

It’s all in the details

Richard Pollack of Needham had one of the odder questions I’ve ever been asked: Are police officers at construction sites required to direct traffic?

You’d think the answer would be yes, but that’s not what Pollack was told after encountering an officer, working a construction detail, who completely ignored him.

“Later, I calmly phoned my community police department to respectfully ask how best to seek an officer’s attention and get help should I ever encounter that kind of situation again,” Pollack told me. “I was told in no uncertain terms that the officers on construction detail were there solely to protect the construction workers and site. Whereas they might — if they so wished to — assist with traffic flow, they were under no obligation to do so. I was advised that in the future I should find another route.”

Pollack said this happened in Needham, so I called Needham Police Chief Phil Droney. He was flabbergasted.

“They are there to direct traffic and to minimize the vehicle safety hazards connected with such work sites,” Droney said. “It’s a dual purpose — protect the workers and direct traffic.”

Droney didn’t know why Pollack was told otherwise. “If it’s a training issue, we’d like to deal with it, and at least follow up and not leave the motorist frustrated,” he said.

Peter DeMarco can be reached at His Facebook page is “Who Taught You to Drive?”and on Twitter @whotaughtU2driv.