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. Why is it a mistake to repeatedly pump the brake pedal on and off for no reason?

   Correct answer: It lets air escape quicker than the compressor can restore, so the brakes fail once pressure gets too low

   Every release lets some air escape; needlessly working the pedal can empty the tanks quicker than the compressor refills them, and once pressure falls too low the brakes stop working.

   Source: Michigan CDL Manual — Section 5.1.7: The Brake Pedal

2. 2. How do you test that the parking brake will hold?

   Correct answer: Set it, then gently tug against it in a low gear to see if it keeps the vehicle from moving

   Stop the vehicle, set the parking brake, and ease against it in a low gear; if it keeps the vehicle from moving, it passes.

   Source: Michigan CDL Manual — Section 5.3.3: Final Air Brake Check

3. 3. If the safety valve on your air system begins letting air escape, what does that indicate?

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

   The safety valve venting air points to a fault in the system, and the problem should be diagnosed and repaired by a mechanic.

   Source: Michigan CDL Manual — Section 5.1.6: Safety Valve

4. 4. When checking a slack adjuster on an s-cam brake, about how much movement at the push-rod point suggests it needs adjustment?

   Correct answer: More than about one inch

   With the parking brake off and the wheels chocked, pull hard on the slack adjuster; if it moves more than roughly one inch where the push rod connects, it probably needs to be adjusted.

   Source: Michigan CDL Manual — Section 5.3.2: Walk-Around Inspection

5. 5. In a dual air system at operating rpm, how long should it take the pressure to climb from 85 up to 100 psi?

   Correct answer: 45 seconds

   A healthy dual system builds from 85 to 100 psi in about 45 seconds at operating rpm; if it climbs too slowly, pressure could fall dangerously low while driving.

   Source: Michigan CDL Manual — Section 5.3.3: Final Air Brake Check

6. 6. With the foot brake fully applied and held for one minute, a combination vehicle's air pressure should not fall by more than how much?

   Correct answer: 4 psi

   Holding the brake applied, a single vehicle may lose up to 3 psi in a minute and a combination up to 4 psi; more than that means leaks to find and fix before driving.

   Source: Michigan CDL Manual — Section 5.3.3: Final Air Brake Check

7. 7. In a spring brake system, what holds the powerful springs back while the vehicle is being driven?

   Correct answer: Air pressure

   While driving, air pressure compresses and holds the springs back; if that air is lost, the springs are freed and they apply the brakes.

   Source: Michigan CDL Manual — Section 5.1.14: Spring Brakes

8. 8. If a truck's air compressor is built with its own separate oil supply, what should the driver do before setting out?

   Correct answer: Check the compressor's oil level

   When the compressor keeps its own oil rather than sharing the engine's, its oil level should be verified before the trip, just like any other fluid check.

   Source: Michigan CDL Manual — Section 5.1.1: Air Compressor

9. 9. In an s-cam drum brake, what happens when the driver presses the brake pedal?

   Correct answer: Air enters the brake chamber, the push rod moves the slack adjuster and turns the s-cam, forcing the shoes against the drum

   Pedal pressure sends air into the brake chamber; the push rod extends, swings the slack adjuster, twists the camshaft, and the S-shaped cam spreads the shoes out against the drum's inner surface.

   Source: Michigan CDL Manual — Section 5.1.8: Foundation Brakes

10. 10. In a dual air brake system, what are the two halves called?

    Correct answer: The primary system and the secondary system

    The two independent halves of a dual system are named the primary and the secondary systems; each keeps its own tanks, hoses, and lines.

    Source: Michigan CDL Manual — Section 5.2: Dual Air Brake

11. 11. Why does an air brake system keep pressurized reservoirs on board?

    Correct answer: They store enough air to work the brakes several times even if the compressor stops

    The storage tanks hold a reserve of compressed air so the brakes can still be applied a number of times even if the compressor quits working.

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

12. 12. What is the job of an alcohol evaporator in an air brake system?

    Correct answer: To cut the chance of ice forming in the brake valves during cold weather

    By feeding alcohol into the air, the evaporator lowers the risk that ice will build up in valves and other parts during cold weather, which could otherwise stop the brakes from working.

    Source: Michigan CDL Manual — Section 5.1.5: Alcohol Evaporator