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 happens to a brake drum if the brakes are used so hard and so long that they overheat?

   Correct answer: Too much heat can cause the brakes to stop working

   Friction at the drum creates heat, and although drums can absorb a lot of it, too much heat can make the brakes quit working.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.8 Foundation Brakes

2. 2. Which factors are added together to make up the total stopping distance for an air brake vehicle?

   Correct answer: Perception, reaction, brake lag, and braking distance

   Total stopping distance for air brakes is perception distance plus reaction distance plus brake lag distance plus braking distance, the brake lag being the extra factor air brakes add.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.4 Stopping Distance

3. 3. On a long, steep downgrade, the braking effect of the service brakes should be treated as what?

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

   On a long or steep downgrade the service brakes are only a supplement to the engine's braking effect; you should already be in a low gear before relying on them.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.6 Proper Braking Technique

4. 4. On the application pressure gauge, needing more and more pressure to hold the same speed is a sign of what, and what should you do?

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

   Rising application pressure to keep a steady speed means the brakes are fading; the correct response is to slow down and shift to a lower gear.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.10 Application Pressure Gauge

5. 5. What causes brake fade from overheating?

   Correct answer: Too much heat changing the lining and expanding the drums

   Excessive heat from overusing the brakes causes chemical changes in the lining that cut friction and makes the drums expand, so the shoes must travel farther and press with less force.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.5 Brake Fading or Failure

6. 6. Using the recommended downgrade braking technique with a "safe" speed of 40 mph, how should you apply the brakes?

   Correct answer: Brake at 40 mph down to about 35 mph, release, then repeat as you speed back up

   You wait until you reach the safe speed of 40 mph, brake hard enough to drop to about 35 mph (roughly five mph below safe speed) over about three seconds, release, and repeat as the speed climbs back.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.6 Proper Braking Technique

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

   Correct answer: The short delay for air to reach the brakes after you press the pedal

   Brake lag is the short delay, about one half second or more, that air brakes take to work after the pedal is pushed, because the air must travel through the lines to the brakes.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.4.4 Stopping Distance