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. When going down a long, steep grade, what is the role of the brakes according to the proper braking technique?

   Correct answer: To assist the engine's own braking effect

   On a long or steep downgrade the brakes serve only to back up the engine's braking effect; once you are in the proper low gear, you brake to feel a firm slowdown, release for a few seconds, and repeat.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.4.6 - Proper Braking Technique Downhill

2. 2. What is brake lag, the extra delay that air brakes add to stopping?

   Correct answer: The short delay while air travels through the lines to the brakes

   Brake lag is the time it takes for the brakes to react after the pedal is pushed; unlike hydraulic brakes that act instantly, air brakes need roughly a half second, sometimes longer, before the air reaches them through the lines.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.4.4 - Stopping Distance

3. 3. At 55 mph on dry pavement, about how long is the total stopping distance for an average driver with good brakes?

   Correct answer: Over 450 feet

   Because air brakes add roughly 32 feet of brake lag distance at 55 mph, the total stopping distance at that speed under good conditions comes to over 450 feet.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.4.4 - Stopping Distance

4. 4. 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 brake vehicles, total stopping distance equals perception distance plus reaction distance plus brake lag distance plus braking distance.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.4.4 - Stopping Distance