Speed & Space Management

Study questions with answers

4 sample Speed & Space Management questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 1. About how much distance does air brake lag add at 55 mph on dry pavement?

   Correct answer: About 32 feet

   At 55 mph on dry pavement, the lag alone adds roughly 32 feet, part of a total stopping distance of over 450 feet.

   Source: Wisconsin Commercial Driver's Manual (BDS356), Section 5.4.4 - Stopping distance

2. 2. On a long, steep downgrade, the service brakes should be used as what?

   Correct answer: Only a supplement to the engine's braking effect

   On a long or steep grade the brakes are only a supplement to the engine's braking effect, so you must first be in the proper low gear.

   Source: Wisconsin Commercial Driver's Manual (BDS356), Section 5.4.6 - Proper braking technique

3. 3. Using the proper braking technique on a downgrade, when do you release the brakes?

   Correct answer: Once your speed is about 5 mph below your safe speed

   You apply just hard enough to feel a firm slowdown, then release once your speed is about 5 mph below your chosen safe speed.

   Source: Wisconsin Commercial Driver's Manual (BDS356), Section 5.4.6 - Proper braking technique

4. 4. What is 'brake lag' in an air brake system?

   Correct answer: The half-second or more it takes air to reach and work the brakes

   Brake lag is the half-second or more it takes for the air to travel through the lines and work the brakes after you press the pedal, unlike instant hydraulic brakes.

   Source: Wisconsin Commercial Driver's Manual (BDS356), Section 5.4.4 - Stopping distance