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 does an air-operated disc brake differ from an s-cam brake?

   Correct answer: It uses a power screw and caliper to clamp a rotor instead of an s-cam

   A disc brake works the chamber and slack adjuster the same way, but instead of an s-cam it uses a power screw that clamps the rotor between caliper pads, much like a large c-clamp.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.8 Foundation Brakes

2. 2. Why is repeatedly pressing and releasing the brake pedal for no reason a bad habit?

   Correct answer: It can use air faster than the compressor can restore it, dropping pressure too low

   Each release lets air out of the system; jabbing the pedal needlessly can drain air faster than the compressor can replace it, and if pressure falls too low the brakes stop working.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.7 The Brake Pedal

3. 3. Where is the ABS malfunction lamp located on a trailer?

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

   Trailers carry the yellow ABS malfunction lamp low on the left side, at the front or rear corner, whereas tractors and buses show it on the instrument panel.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.16 Antilock Braking Systems (ABS)

4. 4. On a long, steep downgrade, the service brakes should be used in what role?

   Correct answer: As a backup that supports the engine's own braking effect

   On a long or steep downgrade the brakes are only a supplement to the engine's braking effect; you get into a proper low gear first and then use the brakes to control speed.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.6 Proper Braking Technique

5. 5. If the air compressor has its own separate oil supply, what should you do before driving?

   Correct answer: Check its oil level

   A compressor that carries its own oil rather than sharing the engine's needs its oil level verified during your pre-trip checks.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.1 Air Compressor

6. 6. On an older truck with a front brake limiting valve set to the 'slippery' position, what happens?

   Correct answer: Front brake air pressure is reduced by about half

   Putting the control in 'slippery' cuts the normal air pressure sent to the front brakes by half; despite the intent, this actually reduces the vehicle's stopping power.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.13 Front Brake Limiting Valve

7. 7. When inspecting brake drums, a crack is too long if it is longer than what?

   Correct answer: Longer than halfway across the width of the friction surface

   A brake drum or disc must not carry a crack that runs longer than halfway across its friction surface; linings must also be free of oil and grease and not worn dangerously thin.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.3.2 Walk-around Inspection

8. 8. On large buses, the low-pressure warning devices commonly signal at what pressure?

   Correct answer: 80 to 85 psi

   While most vehicles warn near 55 psi, it is common for large buses to have their low-pressure warning trigger around 80 to 85 psi.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.11 Low Air Pressure Warning

9. 9. Why can a truck's air brakes still be applied a few times even if the compressor quits working?

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

   The reservoirs stockpile compressed air, so there is a reserve that lets you brake several times before it runs out even with no compressor input.

   Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.3 Air Storage Tanks

10. 10. What does a supply pressure gauge tell the driver?

    Correct answer: How much pressure is stored in the air tanks

    The supply pressure gauge reports how much air pressure is currently stored in the tanks; dual systems use one gauge per half or a single gauge with two needles.

    Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.9 Supply Pressure Gauges

11. 11. What has testing shown about using the front wheel brakes on slippery surfaces?

    Correct answer: Front-wheel skids from braking are unlikely, so front brakes are useful in all conditions

    Front-wheel braking helps in every condition; tests show front-wheel skids from braking are unlikely even on ice, so drivers should not deliberately weaken the front brakes.

    Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.13 Front Brake Limiting Valve

12. 12. Even when a vehicle has an alcohol evaporator, what daily cold-weather task is still required (unless the tanks drain automatically)?

    Correct answer: Draining the air tanks to clear water and oil

    The evaporator only fights ice; you still have to drain the tanks daily to clear out water and oil, and you also top off the alcohol during cold weather.

    Source: Virginia Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.5 Alcohol Evaporator