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. Total stopping distance for an air brake vehicle is made up of four parts. Which set lists them correctly?

   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: South Carolina CDL Manual — Section 5.4.4: Stopping Distance

2. 2. Using proper downgrade braking with a 'safe' speed of 40 mph, how should you use the brakes?

   Correct answer: At 40 mph, brake firmly down to about 35 mph, then release

   Apply firmly enough to feel a definite slowdown, drop to about 5 mph below your safe speed (40 down to 35), release for a few seconds, then repeat as the speed builds back toward 40.

   Source: South Carolina CDL Manual — Section 5.4.6: Proper Braking Technique

3. 3. 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

   Unlike hydraulic brakes that act instantly, air brakes need roughly half a second (sometimes longer) before the air reaches the brakes through the lines, adding brake lag to the total stopping distance.

   Source: South Carolina CDL Manual — Section 5.4.4: Stopping Distance

4. 4. On a long, steep downgrade, what role do the brakes play relative to the engine?

   Correct answer: The brakes only supplement the braking effect of the engine

   Going downhill, braking is only a supplement to engine braking; the vehicle should already be in a low gear before you begin the descent.

   Source: South Carolina CDL Manual — Section 5.4.6: Proper Braking Technique