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. In an s-cam drum brake, what actually slows the vehicle down?

   Correct answer: Friction from the shoes and linings rubbing against the drum

   The shoes and linings are pressed against the inside of the spinning drum, and the friction that results slows the wheel while creating heat.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.8 - Foundation Brakes

2. 2. What best describes a dual air brake system?

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

   A dual air brake system is really two separate air brake systems operated through a single set of brake controls, each with its own tanks and lines.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.2 - Dual Air Brake

3. 3. Why are the air storage tanks important if the compressor suddenly quits working?

   Correct answer: They store enough air to apply the brakes several more times

   The reservoirs hold enough compressed air that the brakes can still be applied several times even after the compressor fails.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.3 - Air Storage Tanks

4. 4. What does the handbook say about braking with the front wheels?

   Correct answer: Front wheel braking is good under all conditions and rarely causes a skid

   Front wheel braking is good under all conditions, and tests show front-wheel skids from braking are unlikely even on ice.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.13 - Front Brake Limiting Valve

5. 5. In a dual air brake system, what are the two systems called?

   Correct answer: Primary and secondary

   One system is called the primary system and the other is called the secondary system.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.2 - Dual Air Brake

6. 6. During a walk-around, how much movement in a manual slack adjuster suggests it needs adjustment?

   Correct answer: More than about one inch

   If a slack adjuster moves more than about one inch where the push rod attaches, it probably needs to be adjusted.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.3.2 - Walk-around Inspection

7. 7. At what pressure is the safety relief valve on the first air tank usually set to open?

   Correct answer: 150 psi

   The relief valve guards the tanks against excess pressure and is normally set to release at 150 psi; if it opens, something needs to be fixed.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.6 - Safety Valve

8. 8. In an air brake system, what does the air compressor do?

   Correct answer: It pumps air into the storage tanks that supply the brakes

   The compressor is the pump that keeps the system supplied with air; it fills the storage tanks that later feed the brakes.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.1 - Air Compressor

9. 9. The governor stops the compressor from adding more air at about what pressure?

   Correct answer: About 125 psi, known as the cut-out level

   The upper limit where pumping shuts off is the cut-out point, which sits near 125 psi.

   Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.2 - Air Compressor Governor

10. 10. On an older vehicle, putting the front brake limiting valve control in the "slippery" position does what?

    Correct answer: It cuts the normal air pressure to the front brakes by half

    In the slippery setting the limiting valve reduces the normal air pressure to the front brakes by half, which actually cuts the vehicle's stopping power.

    Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.13 - Front Brake Limiting Valve

11. 11. At roughly what tank pressure does the governor allow the compressor to start pumping again?

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

    The lower limit where pumping resumes is called cut-in, and it is around 100 psi.

    Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.2 - Air Compressor Governor

12. 12. What is the purpose of an alcohol evaporator on an air brake system?

    Correct answer: It reduces the risk of ice forming in air brake valves in cold weather

    By adding alcohol to the air, the evaporator lowers the chance of ice forming in the valves and other parts during cold weather.

    Source: Colorado Commercial Driver License Manual (DR 2251), Section 5.1.5 - Alcohol Evaporator