Speed & Space Management

Study questions with answers

7 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. Compared with the near-instant action of hydraulic brakes, air brakes need roughly how long for pressure to reach the brakes?

   Correct answer: Half a second or more

   Air brakes have a built-in lag of about a half second or more because the air has to move through the lines before the brakes engage.

   Source: Section 5.4.4 - Stopping Distance

2. 2. Air brakes add which element to total stopping distance that hydraulic brakes do not have?

   Correct answer: Brake lag distance

   Total stopping distance for air brakes is perception plus reaction plus brake lag plus braking distance; brake lag is the extra factor.

   Source: Section 5.4.4 - Stopping Distance

3. 3. For an average driver at 55 mph in good conditions, the total stopping distance with air brakes is about:

   Correct answer: over 450 feet

   Adding perception, reaction, brake lag, and braking distance, the total at 55 mph comes to more than 450 feet.

   Source: Section 5.4.4 - Stopping Distance

4. 4. Before driving a vehicle with a dual air brake system, you should let the compressor build a minimum of:

   Correct answer: 100 psi in both the primary and secondary systems

   Allow time for at least 100 psi to build in both the primary and secondary systems, and watch the gauges before you move.

   Source: Section 5.2 - Dual Air Brake

5. 5. About how much distance does air brake lag add at 55 mph on dry pavement?

   Correct answer: About 32 feet

   At 55 mph on dry pavement, the lag before the brakes act adds roughly 32 feet to the total stopping distance.

   Source: Section 5.4.4 - Stopping Distance

6. 6. If one half of a dual air brake system loses most of its pressure, you should expect that:

   Correct answer: stopping will take longer than normal

   With one system very low, either the front or the rear brakes will not work fully, so it takes farther to stop. Park safely and get it fixed.

   Source: Section 5.2 - Dual Air Brake

7. 7. Why is there a short delay before air brakes grip after the pedal goes down?

   Correct answer: Air needs a moment to travel through the lines to the brakes

   Unlike hydraulic brakes that act at once, air must flow through the lines, so there is a lag of about half a second or more.

   Source: Section 5.4.4 - Stopping Distance