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. If one half of a dual air brake system loses most of its pressure, what happens?

   Correct answer: Either the front or the rear brakes won't work fully, so stopping takes longer

   With one half very low, the brakes it controls (front or rear) will not work fully, which lengthens your stopping distance; stop safely and have the system repaired.

   Source: Michigan CDL Manual — Section 5.2: Dual Air Brake

2. 2. For a vehicle with air brakes, total stopping distance is made up of which factors?

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

   Air brakes add a brake-lag component, so the total is perception distance plus reaction distance plus brake-lag distance plus braking distance.

   Source: Michigan CDL Manual — Section 5.4.4: Stopping Distance

3. 3. What does "brake lag" refer to on a vehicle with air brakes?

   Correct answer: The short delay before the brakes work because the air must travel through the lines

   Unlike hydraulic brakes that act at once, air brakes need a moment (about half a second or more) for the air to travel through the lines and reach the brakes, adding a lag not present on cars.

   Source: Michigan CDL Manual — Section 5.4.4: Stopping Distance

4. 4. At 55 mph on dry pavement, roughly how far is the total stopping distance for an average driver in an air brake vehicle?

   Correct answer: Over 450 feet

   Adding the roughly 32 feet of brake-lag distance at 55 mph, the total stopping distance for an average driver under good conditions works out to more than 450 feet.

   Source: Michigan CDL Manual — Section 5.4.4: Stopping Distance