Question 1

What are the three factors that make up total stopping distance for a commercial vehicle?

Accepted Answer

Perception distance, reaction distance, and braking distance. All three must be added together to find the total stopping distance.

Question 2

At 55 mph on dry pavement, approximately how many feet does it take a fully loaded truck to stop?

Accepted Answer

Approximately 335 feet — significantly longer than a passenger car under the same conditions.

Question 3

How does doubling your speed affect the braking distance of a commercial vehicle?

Accepted Answer

Doubling your speed quadruples your braking distance. This is because braking distance increases with the square of the speed.

Question 4

What is 'perception distance' in the context of stopping distance?

Accepted Answer

Perception distance is the distance your vehicle travels from the moment your eyes see a hazard until your brain recognizes it. The average perception time is 1.75 seconds.

Question 5

What is 'brake lag distance' and how long does it typically take for air brakes to respond?

Accepted Answer

Brake lag distance is the distance traveled between the time you apply the brake pedal and when the brakes actually engage. Air brakes have a lag time of about one-half second.

CDL General Knowledge: Braking & Stopping

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