Commercial Driver License (CDL) Class B Practice Test

If you double your speed, how much will your stopping distance increase?

1. Twice as much

2. Four times as much

3. Three times as much

4. Remains the same

The correct answer is: Four times as much

When you double your speed, your stopping distance increases by a factor of four. This is due to the physics of stopping distance, which is influenced by both the speed of the vehicle and the time required for the driver to react to a situation. The formula for stopping distance includes the reaction distance and braking distance, both of which are affected by speed. The reaction distance is the distance your vehicle travels during the driver's reaction time, which remains proportional to speed. The braking distance, which is the distance needed to come to a complete stop once the brakes are applied, increases with the square of the speed. Therefore, if the speed is doubled, the braking distance becomes four times longer because of the mathematical relationship between speed and stopping distance. This means the overall stopping distance, which combines both the reaction and braking distances, also increases by a factor of four. Understanding this concept is crucial for safe driving, especially in commercial vehicles, where longer stopping distances need to be factored into driving habits and route planning.