Speed & Space Management

Study questions with answers

6 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. On a long, steep downgrade, how should you think about your brakes?

   Correct answer: As a supplement to the braking effect of the engine

   The brakes are only a supplement to the engine's braking effect; you should already be in the proper low gear before using them on a grade.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.6 - Proper Braking Technique

2. 2. What is "brake lag" in an air brake system?

   Correct answer: The delay before air reaches the brakes after you press the pedal

   Brake lag is the short delay (about half a second or more) it takes for air to travel through the lines and make the brakes work after you press the pedal.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.4 - Stopping Distance

3. 3. Total stopping distance for an air-braked vehicle is made up of how many factors?

   Correct answer: Four

   It adds up from four parts: perception distance, reaction distance, brake lag distance, and braking distance.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.4 - Stopping Distance

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

   Correct answer: About 32 feet

   The added brake lag distance at 55 mph on dry pavement is roughly 32 feet, which is why total stopping distance can exceed 450 feet.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.4 - Stopping Distance

5. 5. Using the proper braking technique on a downgrade, when should you release the brakes during each application?

   Correct answer: Once speed drops to about five mph below your safe speed

   Apply firmly enough for a definite slowdown, and once your speed is about five mph below your safe speed, release the brakes; each application should last about three seconds.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.4.6 - Proper Braking Technique

6. 6. The application pressure gauge shows you must keep raising pressure to hold the same speed. What does this usually mean?

   Correct answer: The brakes are fading, so slow down and use a lower gear

   Needing steadily more application pressure to maintain speed is a sign the brakes are fading; you should slow down and shift to a lower gear.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.10 - Application Pressure Gauge