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. Compared with hydraulic brakes, air brakes add 'brake lag.' What is brake lag?

   Correct answer: The short time for air to travel the lines and the brakes to act after you press the pedal

   Unlike hydraulic brakes, which act at once, air brakes need a moment (about half a second or more) for the air to reach the brakes, adding lag to your stop.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance

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

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

   For air brakes the total is perception distance plus reaction distance plus brake-lag distance plus braking distance.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance

3. 3. On a long, steep downgrade, the manual describes the use of the brakes as:

   Correct answer: A backup to the engine's own braking, applied only after you have shifted into a low gear

   Descending, you first pick the proper low gear and let the engine do most of the work; the brakes are used in snubs only to back up that engine braking.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.4.6 Proper Braking Technique

4. 4. If one circuit of a dual air brake system loses most of its pressure, what should you expect?

   Correct answer: Either the front or rear brakes lose power, so stopping takes longer

   With one circuit low, one set of brakes (front or rear) will not do its full share, so your stopping distance grows; stop safely and get it repaired.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.2 Dual Air Brake Systems