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. What is the main job of the air compressor on an air-brake vehicle?

   Correct answer: To force air into the storage reservoirs

   The compressor builds the compressed air the brakes rely on, pushing it into the storage tanks; it is driven off the engine by gears or a belt.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.1 Air Compressor

2. 2. Why is it important to drain the air storage tanks?

   Correct answer: Water and oil collect inside and can harm the system, and the water may freeze in cold weather

   Compressed air carries water and a little oil that settle in the tanks; if left in, the water can freeze and cause brake failure, so the tanks must be emptied.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.4 Air Tank Drains

3. 3. According to the manual, front-wheel braking on an air-brake vehicle is:

   Correct answer: Helpful in all conditions, with front-wheel skids from braking unlikely even on ice

   Testing shows good front-wheel braking helps in every condition and that braking-induced front skids are improbable even on ice, so any limiting control should stay in the normal position.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.13 Front Brake Limiting Valve

4. 4. During the final air-brake check on a dual system, with the engine at operating rpm, about how long should air pressure take to rise between the 85 and 100 psi marks?

   Correct answer: Within 45 seconds

   For dual air systems, air should climb from 85 to 100 psi in roughly 45 seconds at operating rpm; slow buildup signals a problem to fix before driving.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.3.3 Final Air Brake Check - Rate of Air Pressure Buildup

5. 5. As drivers use the brakes and tank pressure drops, at roughly what 'cut-in' pressure does the governor let the compressor start pumping again?

   Correct answer: About 100 psi

   Cut-in is the point where the governor restarts the compressor to rebuild air, typically around 100 psi.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.2 Air Compressor Governor

6. 6. On a vehicle with an application pressure gauge, needing steadily more pressure to hold the same speed is a sign of what?

   Correct answer: The brakes are fading and you should slow down and gear down

   If you must keep raising application pressure just to maintain speed, the brakes are fading; the manual advises slowing down and choosing a lower gear.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.10 Application Pressure Gauge

7. 7. On a vehicle equipped with dual air brakes, how much pressure should build in each circuit before you begin driving?

   Correct answer: 100 psi

   Wait until both the primary and secondary sides reach a minimum of 100 psi before you drive off.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.2 Dual Air Brake Systems

8. 8. The brake pedal in an air-brake vehicle, sometimes called the treadle or foot valve, controls braking how?

   Correct answer: Pressing harder delivers more air pressure to the brakes

   Pushing the pedal down farther applies more air pressure; easing off reduces the pressure and releases the brakes.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.7 The Brake Pedal

9. 9. How can you tell whether an older vehicle came equipped with ABS?

   Correct answer: Read the build date shown on the vehicle's certification label

   The build date on the certification label tells you whether ABS was required; you can also look underneath for the control unit and wheel-speed sensor wiring.

   Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.16 Antilock Braking Systems (ABS)

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

    Correct answer: The S-cam drum brake

    Although wedge and disc designs exist, the S-cam drum brake is by far the most widely used foundation brake.

    Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.8 Foundation Brakes

11. 11. An air-brake vehicle actually contains three braking systems. Which set correctly names them?

    Correct answer: The service, parking, and emergency systems

    Air brakes combine three systems: the service brakes handle everyday stops, the parking brakes hold the vehicle in place, and the emergency brakes can stop it if the others fail.

    Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes) - overview

12. 12. What does an antilock braking system (ABS) do?

    Correct answer: It keeps the wheels from locking up during hard braking so you can stay in control

    ABS is an add-on to the normal brakes that prevents the wheels from locking during hard stops; it may not shorten the stop, but it helps you steer and stay in control.

    Source: North Carolina Commercial Driver License Manual, Section 5 (Air Brakes), 5.1.16 Antilock Braking Systems (ABS)