Which vehicle will have the shortest stopping distance if three identical ones are moving at the same pace but one is on a level surface, one is going uphill and one is heading downhill?

• A. The vehicle travelling on the level surface
• B. The vehicle travelling uphill
• C. The vehicle travelling downhill
• D. All three vehicles will have the same stopping distance

Answer: (B)

Stopping distance is made up of reaction distance plus braking distance, and the reaction part is the same for all three because they’re traveling at the same speed and a same driver takes the same time to react. The difference comes from braking distance, which is affected by gravity on slopes. On an uphill grade, gravity pulls the vehicle back down the slope as you brake, adding to the deceleration already produced by the brakes. That extra pull makes the braking distance shorter. On a downhill grade, gravity helps the vehicle move forward, so braking is less effective and the braking distance becomes longer. On level ground, gravity doesn’t help or hinder braking, so you get the standard braking distance. Therefore, the uphill vehicle will have the shortest stopping distance.