At 55 mph, a fully loaded tractor-trailer requires how many times more stopping distance than a car?

At 55 mph, a fully loaded tractor-trailer requires how many times more stopping distance than a car?

• A. 3x
• B. 2x
• C. 4x
• D. 5x

Answer: (A)

Stopping distance at a given speed comes from two parts: the distance traveled during the driver's reaction and the distance the vehicle itself needs to come to a stop. A fully loaded tractor-trailer has far more mass and momentum than a car, so there’s a lot more energy that must be dissipated when braking. Even with powerful truck brakes, the amount of deceleration available is limited by tire–road friction, and the extra weight means the brakes must work harder to slow the vehicle. The trailer’s inertia adds even more energy that has to be removed, so the overall stopping distance becomes substantially longer than a car’s. Because of these factors, the tractor-trailer’s stopping distance at 55 mph is significantly longer than a car’s, which is why the correct choice describes the truck as needing much more stopping distance.

Stopping distance at a given speed comes from two parts: the distance traveled during the driver's reaction and the distance the vehicle itself needs to come to a stop. A fully loaded tractor-trailer has far more mass and momentum than a car, so there’s a lot more energy that must be dissipated when braking. Even with powerful truck brakes, the amount of deceleration available is limited by tire–road friction, and the extra weight means the brakes must work harder to slow the vehicle. The trailer’s inertia adds even more energy that has to be removed, so the overall stopping distance becomes substantially longer than a car’s. Because of these factors, the tractor-trailer’s stopping distance at 55 mph is significantly longer than a car’s, which is why the correct choice describes the truck as needing much more stopping distance.