Safe Driving Practices

Study questions with answers

12 sample Safe Driving Practices questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 1. In a dual air brake system, which brakes does the primary system typically operate?

   Correct answer: The service brakes on the rear axle or axles

   A dual air brake system uses two separate systems with one set of controls; the primary side normally handles the rear axle service brakes, while the secondary works the front axle and possibly a rear axle.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.2 - Dual Air Brake

2. 2. Which type of foundation brake is the most common on air brake vehicles?

   Correct answer: The s-cam drum brake

   Although wedge and disc brakes exist, the s-cam drum brake is the most common foundation brake found at the wheels.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.8 - Foundation Brakes

3. 3. What is the air compressor's job in the brake system?

   Correct answer: It forces air into the storage tanks or reservoirs

   The compressor's role is to pump air into the storage tanks, or reservoirs, so there is a supply available for braking.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.1 - Air Compressor

4. 4. Which part of the air brake setup operates the brakes every time you press the pedal during ordinary driving?

   Correct answer: The service brake system

   The service brake system is the one that applies and lets off the brakes as you work the brake pedal in normal driving.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5 - What Are Air Brakes

5. 5. What creates the heat that can build up in a drum brake, and why does it matter?

   Correct answer: Friction of the shoes against the drum, and too much heat can make the brakes quit

   The brake presses its shoes and linings onto the drum's inner surface, and the resulting friction produces heat; take on too much heat and the brakes can quit working.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.8 - Foundation Brakes

6. 6. Why is having air storage tanks important on a vehicle with air brakes?

   Correct answer: They hold enough air to brake several times even if the compressor stops

   The tanks store enough compressed air that the brakes can still be applied several times even if the compressor were to quit working.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.3 - Air Storage Tanks

7. 7. As air gets used and tank pressure falls, at roughly what level does the governor let the compressor start pumping again (the cut-in point)?

   Correct answer: About 100 psi

   Once pressure drops to about 100 psi, the cut-in point, the governor allows the compressor to resume building air.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.2 - Air Compressor Governor

8. 8. If an air compressor is built with its own separate oil supply, what should you do before driving?

   Correct answer: Check the compressor's oil level

   A compressor that carries its own oil supply rather than being lubricated by engine oil should have its oil level checked before you set out.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.1 - Air Compressor

9. 9. When checking a slack adjuster on an s-cam brake, how much movement means it should be inspected for proper adjustment?

   Correct answer: More than about one inch

   With the parking brakes off and the wheels chocked, pull hard on the slack adjuster; if it travels beyond roughly one inch at the point where the push rod connects, have it checked for adjustment.

   Source: Maryland Commercial Driver License Manual (DL-151), Section 5.3 - Inspecting Air Brake Systems

10. 10. At about what pressure is the safety relief valve usually set to open, and what does it mean if it lets air out?

    Correct answer: About 150 psi, and releasing air means something needs repair

    The safety relief valve, mounted in the first tank the compressor feeds, is generally set to open near 150 psi; if it vents air, it is a sign something is wrong and a mechanic should look at it.

    Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.6 - Safety Valve

11. 11. At about what pressure does the governor normally stop the compressor from pumping (the cut-out point)?

    Correct answer: Around 125 psi

    The cut-out point, where the governor halts the compressor, is typically around 125 psi.

    Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.2 - Air Compressor Governor

12. 12. Where is the yellow ABS malfunction lamp located on a trailer?

    Correct answer: On the left side of the trailer

    On a trailer the yellow ABS malfunction lamp sits on the left side, at either the front or rear corner, while tractors, trucks, and buses show theirs on the instrument panel.

    Source: Maryland Commercial Driver License Manual (DL-151), Section 5.1.15 - Antilock Braking Systems (ABS)