Your car shares the highways with about 2 million semi tractor-trailer trucks and 13.5 million large commercial trucks. These behemoths can be dangerous to smaller vehicles, considering they weigh 20 to 30 times more than most cars and take up to 40 percent longer to stop.

Their size and maneuverability limitations can make them lethal. In 2013, 3,602 fatal accidents involving semis and large trucks claimed the lives of motorists, pedestrians, bicyclists and trucker drivers, according to the Insurance Information Institute for Highway Safety .

Paul Herbert, a trucking safety and compliance specialist at Western Motor Carrier Safety Institute, Inc. in Quincy, California, offers these tips for sharing the road safely with tractor-trailers.

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Look for the driver’s eyes. Herbert says a large truck or semi tractor-trailer has multiple blind spots on all four sides. The U.S. Department of Transportation’s “Don’t hang out in the No-Zone” campaign illustrates how a truck’s mirrors, even when concaved so the driver can see a wider angle, can’t give the driver the full picture. If you’re driving alongside or to the rear, make sure you can see the driver’s eyes in his side mirrors. If you’re in front, you should be able to see his face in your rear-view mirror.

Tractor-trailer blindspots
Tractor-trailer blind spots (Photo: U.S. Department of Transportation)

“It’s so important to make sure you’re aware of this,” says Herbert, who has been an expert witness in 175 trials and has investigated numerous truck crashes. “The signs on the back of the truck and the mud flaps on big rigs read, ‘If you can’t see my mirrors, I can’t see you.’ But I tell people that if you can’t see my face in the mirror, then I can’t see you.”

Give them a wide berth. Most accidents occur when a vehicle cuts in front of a truck or stops too quickly, Herbert says. State agencies teach truckers to allow one second of distance for every 10 feet of their rig length, plus add an extra second if traveling more than 40 mph. So if a semi is 65 feet long and traveling at 60 mph (about 88 feet per second), the truck should be 660 feet behind you — about the length of two football fields.. Unfortunately truck drivers don’t always follow this rule, says Herbert, especially in traffic or as cars bob in and out of lanes. If you feel a truck is too close, move out of that lane.

Avoid the right-turn squeeze. It’s easy to get caught between a large truck and a stationary object such as a utility pole when a truck turns right. Avoid the area to the right of the vehicle when the truck is turning.

Be extra careful at night. There’s a particular safety issue when tractor-trailers drive at night. Called underride crashes, they are often fatal and usually occur when a truck is backing up or pulling out of a driveway, Herbert explains. Here’s what happens: The front of the truck takes a sharp angle in order to back up the trailer. With the truck’s headlights shining in the oncoming driver’s eyes, he may not see the trailer blocking his lane. By the time the driver sees the trailer in the lane, there’s no time to react and the vehicle can go under the trailer, Herbert says. Experts recommend slowing down and driving cautiously when you see a large truck stopped or moving slowly in the opposite lane.

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Don’t risk a rollover. Trucks have a high center of gravity, and their rollover threshold is about a third that of a passenger car. When a truck is on a highway ramp or driving in high winds, try not to travel next to it. If they exceed their rollover threshold or a strong gust of wind hits the vehicle just right, the semi can tip over.

Let them pass you in the slow lane. In many states, trucks are restricted to the right one or two lanes. If a tractor-trailer is riding your bumper while you’re in the slow lane, the trucker may not have the legal option to pass you on the left. Herbert says drivers should consider moving to a left-hand lane, allowing the rig to pass on the right, and then return to the slower lane.

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Ronald Agrella is a freelance writer and former editor of The Boston Globe’s