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 important to drain the air tanks?

   Correct answer: Water and oil collect inside and can lead to frozen, failing brakes

   Compressed air carries water and oil that gather at the bottom of the tank; if left there, the water can freeze and cause brake failure.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.4 - Air Tank Drains

2. 2. When going down a long, steep grade, the service brakes should be used in what way?

   Correct answer: Only to back up the engine's braking effect, after selecting a low gear

   On a long downgrade, pick a low gear first and use the brakes only to back up the engine's braking, applying and releasing in short intervals.

   Source: Louisiana Commercial Driver's License Manual, Section 5.4.6 - Proper Braking Technique

3. 3. The governor lets the compressor resume pumping at roughly what pressure?

   Correct answer: Around 100 psi, the cut-in level

   When tank pressure drops to around 100 psi, the cut-in point, the governor allows the compressor to start filling the tanks again.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.2 - Air Compressor Governor

4. 4. With the engine off, the parking brake released, and a fully charged system, the air pressure loss for a single vehicle should stay under what rate?

   Correct answer: 2 psi in one minute

   For a single vehicle, the leak-down rate with the brakes released should stay under 2 psi per minute, and under 3 psi for a combination.

   Source: Louisiana Commercial Driver's License Manual, Section 5.3.3 - Final Air Brake Check

5. 5. Which type of foundation brake is the most common on air-brake vehicles?

   Correct answer: The s-cam drum brake

   While wedge and disc brakes exist, the s-cam drum brake is the most widely used foundation brake.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.8 - Foundation Brakes

6. 6. What is the purpose of an alcohol evaporator in an air brake system?

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

   The evaporator adds alcohol to the air, reducing the risk that ice will form in valves and other parts in cold conditions.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.5 - Alcohol Evaporator

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

   Correct answer: Check the compressor's oil level

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

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.1 - Air Compressor

8. 8. In an air brake system, the air compressor is responsible for what?

   Correct answer: Pumping air into the storage tanks that feed the brakes

   The compressor is the pump that keeps the reservoirs charged, supplying the air the brakes rely on.

   Source: Louisiana Commercial Driver's License Manual, Section 5.1.1 - Air Compressor

9. 9. Before driving a vehicle with a dual air system, the compressor should build a minimum of what pressure in both systems?

   Correct answer: 100 psi

   Give the compressor time to reach at least 100 psi in both the primary and secondary systems before you drive.

   Source: Louisiana Commercial Driver's License Manual, Section 5.2 - Dual Air Brake

10. 10. In a drum brake, what actually slows the vehicle?

    Correct answer: The brake shoes and linings pressing against the inside of the drum

    Braking happens when the shoes and linings are forced against the drum's inner surface, creating friction, and heat, that slows the wheel.

    Source: Louisiana Commercial Driver's License Manual, Section 5.1.8 - Foundation Brakes

11. 11. If your ABS stops working, what happens to your braking?

    Correct answer: You still have your normal brakes, so drive normally but get it serviced soon

    ABS is an addition to the regular brakes; if it fails you keep normal braking, though you should have the system serviced soon.

    Source: Louisiana Commercial Driver's License Manual, Section 5.1.16 - Antilock Braking Systems (ABS)

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

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

    A dual system is really two independent air systems, each with its own tanks and lines, operated by one set of controls.

    Source: Louisiana Commercial Driver's License Manual, Section 5.2 - Dual Air Brake