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. What is the job of the air compressor in an air brake system?

   Correct answer: It pumps air into the storage tanks so pressure is available

   The compressor's role is to force air into the storage tanks, keeping a supply of compressed air on hand for the brakes.

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

2. 2. Why is it important to drain the water that collects in the air tanks?

   Correct answer: In freezing weather, that trapped water can turn to ice and knock the brakes out

   Compressed air carries water and a little oil, which settle in the tank bottom; in cold weather that water can freeze and knock out the brakes, so the tanks must be emptied.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.4 Air Tank Drains

3. 3. How does the stop light switch warn drivers behind you that you are braking?

   Correct answer: An air-operated electric switch turns on the brake lights

   An electric switch that is triggered by air pressure turns the brake lights on whenever you apply the air brakes, alerting following drivers.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.1.12 Stop Light Switch

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

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

   A dual air brake system is two separate air brake systems, called primary and secondary, that share a single set of brake controls and each have their own tanks, hoses, and lines.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.2 Dual Air Brake

5. 5. In a dual air system, how quickly should pressure build from 85 to 100 psi when the engine is at operating rpm?

   Correct answer: Within 45 seconds

   On a dual air system at operating rpm, pressure should rise from 85 up to 100 psi in no more than 45 seconds.

   Source: Tennessee Commercial Driver's License Manual, Section 5 (Air Brakes) - 5.3.3 Final Air Brake Check

6. 6. According to the manual, what is the most common problem found during roadside inspections?

   Correct answer: Brakes that are out of adjustment

   Brakes that are out of adjustment are the defect found most often in roadside inspections, which is why checking the slack adjusters matters.

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

7. 7. What can happen if you press and release the brake pedal more than necessary?

   Correct answer: The air is used up faster than the compressor can rebuild it

   Needless fanning of the pedal lets air escape faster than the compressor can replace it, and if pressure drops too low the brakes will not work.

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

8. 8. Why can the brakes still be applied several times even after the air compressor quits working?

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

   The storage tanks hold a reserve of compressed air, enough to allow several brake applications even if the compressor has stopped producing air.

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

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

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

   The supply pressure gauge shows how much air pressure is currently held in the storage tanks.

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

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

    Correct answer: The s-cam drum brake

    Among the foundation brake designs, the s-cam drum brake is the one used most often.

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

11. 11. What is a "wig wag" low air pressure warning device?

    Correct answer: A mechanical arm that drops into view when pressure drops below 55 psi

    A wig wag drops a mechanical arm down into the driver's field of view when system pressure falls below 55 psi, giving a visible low-pressure alert.

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

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

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

    On trailers the yellow ABS malfunction lamp is placed on the left side, either at the front or the rear corner.

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