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 the manual say to test the service brakes at the start of a trip?

   Correct answer: Move ahead slowly at about 5 mph and press the brakes firmly, noting any pull or delay

   Once pressure is back to normal, let off the parking brake, ease forward at roughly 5 mph, and press the brakes firmly, watching for any pull to one side, odd feel, or slow response.

   Source: Ohio CDL Manual — Section 5: Air Brakes

2. 2. On an s-cam brake, what happens when you press the brake pedal?

   Correct answer: The cam rotates and forces the shoes apart against the inside of the drum

   Air enters the brake chamber and drives the rod outward, which shifts the slack adjuster and twists the camshaft. The s-shaped cam then rotates and pushes the shoes apart against the drum's inner surface.

   Source: Ohio CDL Manual — Section 5: Air Brakes

3. 3. With the foot brake fully applied and held for one minute on a combination vehicle, what pressure drop is considered too much?

   Correct answer: More than 4 psi

   For a combination vehicle the applied leakage should not exceed 4 psi in one minute; more than that means you should find and fix the leak before driving.

   Source: Ohio CDL Manual — Section 5: Air Brakes

4. 4. Holding the foot brake down firmly for one minute on a single vehicle, the air loss is too high if the gauge drops more than:

   Correct answer: 3 psi

   With the brakes applied and held for a minute, a single vehicle should not lose more than 3 psi; a combination vehicle should not lose more than 4 psi.

   Source: Ohio CDL Manual — Section 5: Air Brakes

5. 5. Once the governor has stopped the compressor, tank pressure must fall to about what level before the compressor is allowed to start pumping again (the "cut-in" point)?

   Correct answer: About 100 psi

   The governor lets the compressor start again when pressure drops to roughly 100 psi, then it builds back up toward the cut-out level near 125 psi.

   Source: Ohio CDL Manual — Section 5: Air Brakes

6. 6. On older trucks with a front brake limiting valve control marked "normal" and "slippery," where should the control usually be kept?

   Correct answer: In the "normal" position, because front-wheel braking is good in all conditions

   It should stay in the "normal" position. Front-wheel braking is good in all conditions and skids from braking are unlikely even on ice; the "slippery" setting only reduces stopping power.

   Source: Ohio CDL Manual — Section 5: Air Brakes

7. 7. Automatic slack adjusters are found on all vehicles built since what year?

   Correct answer: 1994

   Every vehicle built since 1994 has automatic slack adjusters. Even so, they still need to be checked, because excessive pushrod stroke points to a mechanical problem.

   Source: Ohio CDL Manual — Section 5: Air Brakes

8. 8. Why does the Ohio manual stress that you must drain the air tanks?

   Correct answer: Water and oil collect inside and the water can freeze and cause brake failure

   Compressed air carries water and a little compressor oil, which settle at the bottom of the tanks. Left there, that moisture can turn to ice when it is cold and knock the brakes out.

   Source: Ohio CDL Manual — Section 5: Air Brakes

9. 9. Which type of foundation brake is the most common at each wheel?

   Correct answer: The s-cam drum brake

   The s-cam drum brake is the most common foundation brake. Wedge brakes and disc brakes are used less often.

   Source: Ohio CDL Manual — Section 5: Air Brakes

10. 10. An air brake setup is really three separate braking systems working together. Which three does the Ohio manual describe?

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

    Air brakes combine a service brake system used with the pedal in normal driving, a parking brake system, and an emergency brake system that borrows parts of the other two to stop the vehicle if the brakes fail.

    Source: Ohio CDL Manual — Section 5: Air Brakes

11. 11. During the final air-brake check, at roughly what pressures should the compressor cut in and cut out?

    Correct answer: Cut in near 100 psi and cut out near 125 psi

    The compressor should start pumping (cut in) at about 100 psi and stop (cut out) at about 125 psi. If the governor doesn't behave this way, it may need repair.

    Source: Ohio CDL Manual — Section 5: Air Brakes

12. 12. In a dual air system at operating rpm, how long should it take for pressure to rise from 85 up to 100 psi?

    Correct answer: 45 seconds

    At operating rpm, a dual system should climb from 85 up to 100 psi in roughly 45 seconds. If it fills too slowly, pressure could fall too low while driving.

    Source: Ohio CDL Manual — Section 5: Air Brakes