Speed & Space Management

Study questions with answers

5 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. Which four elements add up to the total stopping distance of 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 extra lag term being what sets air brakes apart.

   Source: New Jersey Commercial Driver License Manual, Section 5.4 - Stopping Distance

2. 2. On a long, steep downgrade, how should the service brakes be used relative to the engine?

   Correct answer: Only to back up the slowing effect the engine already provides

   Going downhill, the brakes are only a supplement to engine braking; once in the proper low gear you apply them firmly enough to feel a clear slowdown, then release once you are a few mph below your safe speed, repeating as needed.

   Source: New Jersey Commercial Driver License Manual, Section 5.4 - Proper Braking Technique

3. 3. In a dual air brake system, what happens to your stopping if one of the two systems loses most of its pressure?

   Correct answer: It will take longer to stop because part of the brakes won't work fully

   If one circuit drops very low, part of the braking (front or rear) won't be doing its full job, so stopping takes more distance; pull over and have it repaired.

   Source: New Jersey Commercial Driver License Manual, Section 5.2 - Dual Air Brake Systems

4. 4. How does "brake lag" make air brakes different from the hydraulic brakes on a car?

   Correct answer: Air takes extra time to travel the lines, delaying when the brakes grab

   Hydraulic brakes act almost instantly, but with air brakes it takes a fraction of a second (about half a second or more) for the air to travel the lines and reach the brakes, adding a lag to total stopping distance.

   Source: New Jersey Commercial Driver License Manual, Section 5.4 - Stopping Distance

5. 5. You must keep increasing brake application pressure to hold the same speed. What is likely happening, and what should you do?

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

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

   Source: New Jersey Commercial Driver License Manual, Section 5.1.10 - Application Pressure Gauge