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. How are spring brakes held in the released position while you drive?

   Correct answer: By air pressure holding the springs back

   During driving, air pressure holds the powerful springs back; if that air is lost, the springs are freed and clamp the brakes on.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.14 - Spring Brakes

2. 2. How does ABS affect your normal stopping distance?

   Correct answer: It does not necessarily shorten stopping distance but helps you stay in control

   ABS won't automatically give you a shorter stop; its true value is letting you hold the rig steady and under control while braking hard.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.16 - Antilock Braking Systems

3. 3. At roughly what tank pressure does the governor normally stop the compressor from pumping (the cut-out point)?

   Correct answer: Around 125 psi

   When tank pressure climbs to about 125 psi, the governor reaches its cut-out setting and shuts the compressor off so pressure does not keep rising.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.2 - Air Compressor Governor

4. 4. On a trailer, where would you look for the yellow ABS malfunction lamp?

   Correct answer: On the left side, at the front or rear corner

   While tractors, trucks, and buses show the yellow ABS malfunction lamp on the dash, on trailers the lamp is placed on the left side, at either the front or rear corner.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.16 - Antilock Braking Systems

5. 5. When does an antilock braking system actually do anything?

   Correct answer: Only when a wheel is on the verge of locking up

   ABS is an add-on to your regular brakes and stays out of the way until a wheel is about to lock up, at which point it steps in to prevent the lockup.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.16 - Antilock Braking Systems

6. 6. What best describes a dual air brake system?

   Correct answer: Two separate air brake circuits sharing one set of controls

   A dual system is two independent air brake circuits, each with its own tanks and lines, operated through one set of brake controls for safety.

   Source: New Jersey Commercial Driver License Manual, Section 5.2 - Dual Air Brake Systems

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

   Correct answer: It builds and pushes air into the storage reservoirs

   The compressor's role is to pump air into the storage tanks (reservoirs) so there is always pressure available to work the brakes.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.1 - Air Compressor

8. 8. At about what pressure does the governor let the compressor begin pumping again (the cut-in point)?

   Correct answer: About 100 psi

   Once tank pressure falls to roughly 100 psi, the governor's cut-in setting lets the compressor resume building air back up.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.2 - Air Compressor Governor

9. 9. Why should you avoid pressing the brake pedal while the spring brakes are already applied?

   Correct answer: The combined spring and air forces can damage the brakes

   Adding air pressure on top of the springs stacks both forces on the brakes, which can damage them; it is best to make a habit of never pushing the pedal when the spring brakes are set.

   Source: New Jersey Commercial Driver License Manual, Section 5.1.15 - Parking Brake Controls

10. 10. Why is repeatedly pressing and releasing the brake pedal for no reason a problem?

    Correct answer: It can drain air faster than the compressor replaces it, lowering pressure too far

    Each release lets compressed air escape; jabbing the pedal needlessly can bleed air out faster than the compressor can refill it, and if pressure drops too far the brakes stop working.

    Source: New Jersey Commercial Driver License Manual, Section 5.1.7 - The Brake Pedal

11. 11. 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: New Jersey Commercial Driver License Manual, Section 5.1.8 - Foundation Brakes

12. 12. How much pressure should build up in a dual air brake system before you start driving?

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

    You should give the compressor time to reach at least 100 psi in both the primary and secondary systems before you move the vehicle.

    Source: New Jersey Commercial Driver License Manual, Section 5.2 - Dual Air Brake Systems