Under ideal conditions, a truck with air brakes going 55 mph would require a stopping distance of more than how many feet?

Under ideal conditions, a truck with air brakes going 55 mph would require a stopping distance of more than how many feet?

• A. Less than 100 feet
• B. About 200 feet
• C. More than 300 feet
• D. About 500 feet

Answer: (C)

Stopping distance for a heavy vehicle rises quickly with speed and is the sum of perception/reaction distance and braking distance. For a tractor-trailer with air brakes, even in ideal conditions, you have to account for the time it takes to perceive a hazard and react, plus the braking distance needed to dissipate the vehicle’s large kinetic energy. At 55 mph, the reaction distance is substantial, and the braking distance on dry pavement with a loaded truck is already considerable because the brakes must slow a very heavy mass. When you add the brake-pressure build-up time that air brakes require, the total grows larger still. Put together, the typical total stopping distance at that speed is over 300 feet, so the correct conclusion is that more than 300 feet are required.

Stopping distance for a heavy vehicle rises quickly with speed and is the sum of perception/reaction distance and braking distance. For a tractor-trailer with air brakes, even in ideal conditions, you have to account for the time it takes to perceive a hazard and react, plus the braking distance needed to dissipate the vehicle’s large kinetic energy. At 55 mph, the reaction distance is substantial, and the braking distance on dry pavement with a loaded truck is already considerable because the brakes must slow a very heavy mass. When you add the brake-pressure build-up time that air brakes require, the total grows larger still. Put together, the typical total stopping distance at that speed is over 300 feet, so the correct conclusion is that more than 300 feet are required.