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. Which style of foundation brake is the most common on air-braked vehicles?

   Correct answer: The S-cam drum brake

   While wedge and disc types exist, the S-cam drum brake is by far the most common foundation brake.

   Source: Arizona CDL Manual — Section 5.1.8: Foundation Brakes

2. 2. On vehicles with an automatic front-wheel limiting valve, when is full air pressure allowed to reach the front brakes?

   Correct answer: Only during very hard braking, about 60 psi of application pressure or more

   An automatic front-wheel limiting valve holds back some front air except during very hard applications of roughly 60 psi or more; the driver cannot control it.

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

3. 3. If one half of a dual air brake system loses most of its pressure, what should you expect?

   Correct answer: One end of the vehicle, front or rear, will not brake fully, so stopping takes longer

   With one side very low, only part of the braking, either the front or the rear, still works, which lengthens your stop; bring it to a safe halt and have it repaired.

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

4. 4. Why is it important to let the water out of the air tanks, especially before cold weather?

   Correct answer: Water sitting in the tanks can freeze and cause the brakes to fail

   Compressed air carries moisture and a little compressor oil that settle in the tanks; in the cold the water can freeze and knock out the brakes, so the tanks must be drained.

   Source: Arizona CDL Manual — Section 5.1.4: Air Tank Drains

5. 5. Which brake-related defect is cited as the most common problem found during roadside inspections?

   Correct answer: Brakes that are out of adjustment

   Out-of-adjustment brakes top the list of roadside inspection findings and make a vehicle much harder to stop, which is why checking the slack adjusters matters.

   Source: Arizona CDL Manual — Section 5.3: Inspecting Air Brake Systems

6. 6. During inspection, a brake drum should be replaced if it has a crack longer than what?

   Correct answer: Half the width of the friction surface

   Drums or discs must not have a crack longer than half the width of the friction surface; linings must also be secure, not oil-soaked, and not dangerously thin.

   Source: Arizona CDL Manual — Section 5.3: Inspecting Air Brake Systems

7. 7. What does an alcohol evaporator do for an air brake system in winter?

   Correct answer: It reduces the chance of ice forming inside the brake valves

   The evaporator feeds alcohol into the air to cut down on ice forming inside valves and other parts during cold weather; you still have to drain the tanks daily.

   Source: Arizona CDL Manual — Section 5.1.5: Alcohol Evaporator

8. 8. At roughly what tank pressure does the governor reach its cut-out point and stop the compressor from loading more air?

   Correct answer: Near 125 psi

   The cut-out is about 125 psi; once the tanks reach that level the governor stops the compressor so the system does not over-pressurize.

   Source: Arizona CDL Manual — Section 5.1.2: Air Compressor Governor

9. 9. Why can you still apply the brakes a few times even if the air compressor quits working?

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

   The reservoir tanks store compressed air, so a driver has enough for several brake applications even after the compressor stops.

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

10. 10. What is the purpose of the electric heating element offered on some automatic tank drains?

    Correct answer: To keep the automatic drain from freezing in cold weather

    Automatic drains can be fitted with electric heaters so the drain itself does not freeze up when temperatures fall.

    Source: Arizona CDL Manual — Section 5.1.4: Air Tank Drains

11. 11. Air brakes are described as a combination of three braking systems. Which set correctly names all three?

    Correct answer: Service brakes, parking brakes, and emergency brakes

    A vehicle's air brake setup is really three systems in one: the service system you work with the pedal, the parking system you set with a hand control, and the emergency system that borrows parts of the other two to stop you if something fails.

    Source: Arizona CDL Manual — Section 5: Air Brakes

12. 12. The safety relief valve on the first air tank is normally set to open at about what pressure?

    Correct answer: About 150 psi

    Mounted on the first tank the compressor feeds, the safety valve typically vents at 150 psi to guard the system against over-pressure.

    Source: Arizona CDL Manual — Section 5.1.6: Safety Valve