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

   Correct answer: Only as a supplement to the engine's braking, while in a proper low gear

   On a steep grade the brakes should only supplement engine braking - be in a proper low gear and apply them in short intervals.

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

2. 2. Compared with hydraulic brakes, why do air brakes add 'brake lag' to the stopping distance?

   Correct answer: It takes a half second or more for the air to reach the brakes through the lines

   Unlike hydraulic brakes, which work instantly, air needs about a half second or more to travel through the lines to the brakes.

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

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

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

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

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

4. 4. At 55 mph on dry pavement, roughly how far does an average air brake vehicle travel before it fully stops?

   Correct answer: More than 450 feet

   Adding the brake lag (about 32 feet) to the other factors, the total stopping distance at 55 mph works out to more than 450 feet.

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