Speed & Space Management

Study questions with answers

7 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. What causes brake fade?

   Correct answer: Too much heat from overuse, which reduces lining friction and expands the drums

   Fade comes from too much heat: overuse changes the lining chemically and cuts its friction, and it expands the drums.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.5 - Brake Fading or Failure

2. 2. When using proper (snub) braking on a long downgrade, the brakes serve as what?

   Correct answer: A supplement to engine braking, after you are in the proper low gear

   On a long grade the brakes only back up the engine's braking, and you select a low gear first.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.6 - Proper Braking Technique

3. 3. Total stopping distance for an air brake vehicle is made up of which four parts?

   Correct answer: The perception and reaction distances, plus the brake-lag and braking distances

   Total stopping distance combines the perception, reaction, brake-lag and braking distances.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.4 - Stopping Distance

4. 4. At 55 mph in good conditions, the total stopping distance for an air brake vehicle is greater than about how many feet?

   Correct answer: More than 300 feet

   At 55 mph in good conditions, the total stopping distance works out to more than 300 feet.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.4 - Stopping Distance

5. 5. What is 'brake lag' on an air brake system?

   Correct answer: The brief delay while air moves through the lines before the brakes take hold

   Brake lag is the short delay while air travels through the lines before the brakes begin to act.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.4 - Stopping Distance

6. 6. In the snubbing technique, once you have braked to about 5 mph below your safe speed, what do you do next?

   Correct answer: Let off the brakes, then reapply once you return to your safe speed

   You brake to roughly 5 mph under your safe speed, let off for about three seconds, then reapply when you climb back to that speed.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.6 - Proper Braking Technique

7. 7. On dry pavement at 55 mph, about how much distance does air brake lag add?

   Correct answer: Roughly 32 feet

   At 55 mph on dry pavement, air brake lag adds roughly 32 feet to the stop.

   Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.4 - Stopping Distance