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While I was driving on the highway one day, a Hannaford Supermarkets 18-wheeler came trucking past me in the right lane. Soon his left turn signals began flashing, so I eased up on my gas pedal to let him in front of me — a courteous gesture, I thought.

So why was my dad, sitting next to me, tapping so vigorously on my shoulder?

“Flash your lights,” he said.

I cast him a questioning glance. Why would I do that?

“Hold the headlights off to a count of three, then put them on to bring him over,” he said. “The minute you flash your lights, it’s so much easier for him to pass. That’s the signal for trucks. Do it when he’s about four car lengths past you.”

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Truck drivers, my dad explained, sometimes have a difficult time judging how much distance they have between the back of their trailer — frequently some 40 feet long — and the car that’s directly behind them. It’s usually not a problem on a sunny day, but poor road lighting or the glare of headlights at night, or splashing water (it was raining at the time) can create uncertainty, even for veteran truckers.

My dad would know: He’s a big-rig driver himself.

My impromptu lesson in trucker etiquette got me thinking about what else the average Ford Escape, Lexus GS, or Toyota Prius owner doesn’t know about driving a big rig.

For insight, I approached some true authorities: Mark Greenberg and Don Lane of the Quincy-based New England Tractor Trailer Training School, and Trooper Mike Short, of the State Police’s Commercial Vehicle Enforcement Section.

Why don’t trucks go faster?

I was passed by a truck the day I was with my dad, but usually it’s the other way around. Rarely do I see any large vehicle going faster than 60 or 65 miles an hour; very often, they’re moving slower than most traffic .

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It’s a far cry from the movies I grew up watching, such as “Smokey and the Bandit,” where truckers “put the hammer down” and broke every speeding law on the books.

Short, a 23-year veteran of the State Police’s truck unit, and a former trucker himself, assured me that commercial operators still get plenty of speeding tickets, partly because of the pressure they face to deliver loads on time. But the trucking industry has greatly changed in recent decades, he said, as stiffer federal regulations and penalties have made speeding more costly.

“A lot of companies are governing their trucks to 65 m.p.h. because they are worried about violations, and also fuel efficiency,” Short said. “A lot of people can’t understand that a truck just can’t go faster than that. Even if it’s governed at 65, the driver doesn’t have the same pedal you do in a car, so he might only be able to get it up to 60.”

Lane said modern trucks are designed to reach peak efficiency at speeds between 55 and 65 m.p.h. “We teach all of our drivers to drive at the posted speed limit,” he said.

Some states, such as Connecticut, fine commercial operators more for speeding than they do other drivers. Massachusetts doesn’t, but a trucker who gets pulled over for speeding also runs the risk of being cited for dozens of violations pertaining to vehicle weight, brakes, lights, and beyond that could double or triple the total fine.

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Danger of an empty truck

What will come to a stop faster, a train engine pulling two cars, or one that’s pulling 20? Common sense says the one with less weight behind it.

That logic doesn’t apply to big rigs, however. It’s actually easier for a driver to stop a fully loaded truck weighing 80,000 pounds, Greenberg says, than it is to stop a truck whose trailer is empty, or a truck that isn’t towing a trailer at all.

“When you’re not pulling a trailer, it’s called ‘riding bobtail.’ That’s the most dangerous,” he said.

When a truck is loaded, thousands of pounds of weight rest on its axles. That’s a good thing because the weight pushes the wheels firmly to the ground, creating more traction.

“The heavier the vehicle, the more work the brakes must do to stop it,” reads the Registry of Motor Vehicles’ Commercial Driver’s License Manual. “But the brakes, tires, springs, and shock absorbers on heavy vehicles are designed to work best when the vehicle is fully loaded. Empty trucks require greater stopping distances because an empty vehicle has less traction. You can’t steer or brake a vehicle unless you have traction.”

When a truck is empty, or without a trailer, its rear tires can lift off the ground when the vehicle’s front brakes are suddenly applied. It’s a bit like when you’re pedaling fast on a bicycle and apply just the front brakes: you’re apt to flip over.

Of course, it’s also very tough for a big-rig driver to stop a fully loaded truck, especially when cut off by a car darting in front of him. The state manual estimates that a loaded truck driving at 55 m.p.h. needs about 290 feet — roughly the length of a football field — to come to a complete stop. Wet roads “can double stopping distance.”

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Trucks have blind spots

Flashing your lights to let a trucker into your lane is a nice thing to do, but what a big-rig driver wants more than anything is for you to avoid his blind spots. A typical 18-wheeler has a scary number of them — so many that the Federal Motor Carrier Safety Administration has a public service campaign about blind spots, dubbing them the “No-Zones” of a truck.

No matter how many mirrors a big rig has, its driver very likely can’t see you when your vehicle is:

1. Left of the big rig, with the nose of your car just behind where the driver is sitting

2. Right of the big rig, about the same position. But this blind spot is bigger, extending two or even three lanes to the right of the truck

3. Directly in front of the big rig

4. Directly behind the big rig

It’s impossible to avoid all of a truck’s No-Zones, particularly when you’re in thick traffic. The key is to get out of them as quickly as you can.

Short tells disturbing stories of motorists who unwittingly linger in a trucker’s blind spots, then get run over when the truck turns in their direction.

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“I had a case where there was a woman driving on Route 128 south. She was in [the trucker’s] blind spot when he turned to take the exit, and he dragged her car 100 yards sideways,” Short said. “He didn’t even know he had hit her until he looked in his mirror and saw pieces of her car flying on the road.”


Peter DeMarco can be reached at his new e-mail address, peter.demarco@globe.com. His Facebook page is “Who Taught You to Drive?”and on Twitter @whotaughtU2driv.