Who taught YOU to drive?

A few more snow questions as winter ends

A snowplow clears Shirley Street in Winthrop during the early February blizzard.Plow blades are supposed to be angled, to lessen the plow’s width as it travels on the road.
Darren McCollester/Getty Images
A snowplow clears Shirley Street in Winthrop during the early February blizzard.Plow blades are supposed to be angled, to lessen the plow’s width as it travels on the road.

The winter of 2013 officially ends Wednesday, so let us send it off with some final thoughts on snow-related driving. It is hard to believe we were shoveling out just over a week ago.

Strange strobes

During blizzard week, I kept encountering bright strobing lights at various traffic intersections, especially early in the morning. What are these strange strobes? How should drivers react to them? And why did I see so many of them going off that week?

I gathered they had something to do with fire trucks’ ability to trigger green lights for themselves — and I was right.


“They are called traffic preemption devices,” said Jennifer Mieth, public information officer for the state Department of Fire Services. “They are for emergency vehicles, generally larger pieces of apparatus like fire trucks, to clear intersections. The new models — which you seem to be referring to — receive the signal at quite a distance. So folks might not see a big red truck or hear the siren yet as they’re seeing the strobes.”

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Bell Traffic Signal Maintenance Co. of Weymouth has been installing traffic signals for 42 years, including preemption devices. When emergency responders need to trigger a green light, they simply flash a strobe of their own, said Janine Gill, company treasurer.

Sometimes that strobe is on the vehicle’s roof; sometimes it is mounted on the front grille as a spinning, circular wheel; sometimes the strobe is hand-held by someone sitting in the passenger seat. When a sensor mounted on or near a traffic light “catches” the strobe, it triggers a green light.

The strobe lights at intersections actually have nothing to do with the actual triggering process. Their purpose is to inform whoever is driving the police car or fire truck that the preemption was successful, and that drivers in every other direction have been given a red light, Gill said.

As for why I saw them so frequently during the blizzard week, she offered two possible explanations: either there were a lot of emergency calls during that time, or the preemption devices I happened to encounter were malfunctioning.


“These are electrical components,” she said. “A signal could have gotten twisted around, there could have been a crimped wire or something that caused the lights to go to emergency flash. It may have been a short in the field. We did have a blizzard. There [were] a lot of intersections out completely with no power, or flashing [incorrectly] because someone had knocked down a traffic light.”

Beyond a ban

Governor Deval Patrick was able to order a driving ban during the blizzard thanks to a state statute known as the Civil Defense Act of 1950. But he need not have stopped there, said police instructor and attorney John Sofis Scheft, whose consulting business, Law Enforcement Dimensions, is based in Arlington.

“This was a law passed in the heart of the Cold War, Korea, duck and cover, radioactive shelters, etc.,” he said in an e-mail.  “They were worried about a lot more than flooding, or bad visibility on the Pike. So the governor was given extraordinary powers.”

For example, if Patrick had wanted to allow snowmobiles to use public roads, he could have done so by suspending the need for vehicles to have license plates. (State Police, in fact, had reports of snowmobilers illegally zipping along some roads.) Or he could have ordered every speed-limit sign in the state to be covered, giving police complete discretion over speed limits.

My suggestion for the next driving ban? Suspend the need for emergency responders and plow operators to wait for red lights.


As I wrote last week, I was out in a plow truck during the storm, and nothing seemed sillier than waiting for a light to change when I had not seen another vehicle for miles. Slowing down and proceeding with caution, which is the rule when lights are malfunctioning, would have sufficed.

Plow-blade math


From experience, I know how far my snowplow blade is from another vehicle, just as a car driver would know how far their front bumper is from another vehicle. But I also understand how scary it is to see a huge piece of steel swinging toward your windshield. So what is the average buffer zone between a plow blade and a car, in terms of actual feet and inches?

A typical pickup truck is about 6½ feet wide. If an 8-foot-wide plow blade is attached to that truck, which is a fairly standard length, the truck is for all practical purposes 8 feet wide.

But remember, drivers are supposed to angle their blades, said Bill Casale, senior vice president and partner of Brake & Clutch Inc. on Bridge Street in Salem, which has sold Fisher-brand snowplow blades for decades.

“When an 8-foot snow plow blade is angled, it [becomes] 7-feet, 1-inch wide,” he said. “At that point, it only sticks out maybe 3 inches past each side of the vehicle.”

So that is all that plow driver has to compensate for: 3 additional inches.

Most street lanes are at least 10-feet wide, with some as wide as 12 feet, and a few as narrow as 9 feet. Using 10 feet as an average, that puts a pickup-truck plow blade about 1.5 feet from the center line. That is a decent buffer zone.

Of course, there are also pickup trucks that carry 9-foot plow blades. I own one, in fact. Do those longer plow blades pose a greater danger to a car?

When fully angled, a 9-foot blade is 7-feet, 11-inches wide, which means it is 5 inches closer to a car. But again, when angled, most 9-foot plows protrude only about 3 inches beyond the width of the vehicle, Casale said, as 9-foot blades are found on wider, heavier trucks.

The caveat, of course, is that streets become narrower than usual with large amounts of snow. When driving lanes shrink to 8 or 9 feet wide, the buffer zone disappears, and an oncoming snowplow blade might very well be on the other side of the center line. That means everyone should proceed with extra caution.

Plow drivers who do not angle their blades — assuming there is no mechanical problem — just aren’t thinking. By law, anyone with a blade 9 feet or longer is supposed to angle it, Casale said.

“The United States Department of Transportation mandates that a vehicle can’t be any wider than 102 inches,” he said. “If you had a 9-foot snowplow blade positioned perfectly straight, it’s going to be 108 inches wide. Technically, that truck is too wide to drive down the roadway.”

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