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. If the safety valve begins letting air escape, what does that indicate?

   Correct answer: Something is wrong and a mechanic should fix it

   The safety valve should not normally vent air; if it does, there is a fault that a mechanic needs to correct.

   Source: Massachusetts CDL Manual — Section 5.1.6: Safety Valve

2. 2. An automatic front-wheel limiting valve reduces air to the front brakes except when what happens?

   Correct answer: The brakes are applied very hard — about 55 psi or more of application pressure

   These automatic valves hold back front-brake air except during very hard applications of roughly 55 psi or more, and the driver cannot control them.

   Source: Massachusetts CDL Manual — Section 5.1.13: Front Brake Limiting Valve

3. 3. How is the air compressor usually driven on an air-brake vehicle?

   Correct answer: The engine turns it through gears or a v-belt

   The compressor is turned by the engine, linked to it by gears or a v-belt, and it may be cooled by air or by the engine's cooling system.

   Source: Massachusetts CDL Manual — Section 5.1.1: Air Compressor

4. 4. If the air compressor has its own supply of oil, what should you check before driving?

   Correct answer: The compressor's oil level

   A compressor with a separate oil supply needs its oil level checked before you drive, just as you would check engine oil.

   Source: Massachusetts CDL Manual — Section 5.1.1: Air Compressor

5. 5. Air brakes actually combine three separate braking systems. Which answer names all three correctly?

   Correct answer: Service, parking, and emergency brakes

   An air-brake vehicle relies on three systems that share components: the service brakes for everyday stopping, the parking brakes, and the emergency brakes that can stop the vehicle if part of the system fails.

   Source: Massachusetts CDL Manual — Section 5: Air Brakes

6. 6. What is the role of the service brake system?

   Correct answer: It applies and releases the brakes with the pedal during ordinary driving

   The service brake system is what you use for normal driving; pressing the pedal applies the brakes and letting off releases them.

   Source: Massachusetts CDL Manual — Section 5: Air Brakes

7. 7. How do air-operated disc brakes differ from s-cam brakes?

   Correct answer: They use a power screw rather than an s-cam to clamp the rotor

   Disc brakes act through a power screw that clamps the rotor between caliper pads, in place of the s-cam used in drum brakes.

   Source: Massachusetts CDL Manual — Section 5.1.8: Foundation Brakes

8. 8. Which statement about antilock brakes (ABS) is accurate?

   Correct answer: ABS may not reduce how far you take to stop, but it helps you stay in control when braking hard

   ABS is an add-on to the normal brakes and works only when a wheel is about to lock; it will not always shorten the stop, but it helps you keep control.

   Source: Massachusetts CDL Manual — Section 5.1.16: Antilock Braking Systems

9. 9. Why can you still apply the brakes a few times after the compressor quits?

   Correct answer: The storage tanks keep a reserve of compressed air

   Air tanks store enough compressed air to allow several brake applications, giving you a reserve if the compressor fails.

   Source: Massachusetts CDL Manual — Section 5.1.3: Air Storage Tanks

10. 10. What is a dual air brake system?

    Correct answer: Two separate air brake systems that share a single set of brake controls

    A dual system has two independent air systems, a primary and a secondary, each with its own tanks and lines, run by one set of controls.

    Source: Massachusetts CDL Manual — Section 5.2: Dual Air Brake Systems

11. 11. While you are driving normally, what keeps the powerful springs of the spring brakes from applying the brakes?

    Correct answer: Air pressure holding the springs back

    Air pressure compresses and holds the springs back; if that air is lost, the springs apply the brakes.

    Source: Massachusetts CDL Manual — Section 5.1.14: Spring Brakes

12. 12. Which foundation brake is the most common on air-brake vehicles?

    Correct answer: The s-cam drum brake

    The s-cam drum brake is the type you will most often find; wedge and disc designs are less common.

    Source: Massachusetts CDL Manual — Section 5.1.8: Foundation Brakes