California CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

Your service brakes stop working on a mountain downgrade because they have overheated and faded. What is your best option?

Accepted Answer

Use an escape ramp if one is available — Use an escape ramp if one is available. Escape ramps are built on many steep grades to safely stop runaway vehicles using a long bed of loose material or an upgrade, and using one avoids a far worse crash.

Answer

Swerve from side to side to scrub off speed

Answer

Shift into neutral so the drivetrain cannot push the vehicle

Answer

Steer onto the shoulder and hold the horn down

Question 2

What is "controlled braking" in an emergency stop?

Accepted Answer

Braking as hard as possible without locking the wheels — Controlled braking means applying the brakes as hard as you can without locking the wheels. Keep steering movements very small while braking this way; if you need to make larger steering adjustments or the wheels lock, release the brakes, then reapply.

Answer

Braking only with the trailer hand valve

Answer

Locking the wheels intentionally to scrub off speed

Answer

Using the parking brake and service brake together

Question 3

The low air pressure warning comes on while you are driving. What should you do?

Accepted Answer

Stop and safely park as soon as possible — Stop and safely park as soon as possible. If air pressure keeps dropping, the spring brakes will come on by themselves, and you could lose controlled braking — it is safer to stop while you still have control.

Answer

Continue to the next truck stop and have the system checked

Answer

Pump the brake pedal to build the pressure back up

Answer

Downshift and rely on engine braking for the rest of the trip

Question 4

Air brakes are really three braking systems in one. Which of them stops the vehicle if the brake system fails, using parts of the other two?

Accepted Answer

The emergency brake system — The service brakes work from the pedal in normal driving, and the parking brakes work from the parking control. The emergency brake system borrows parts of both to stop the vehicle when the brake system fails.

Answer

The service brake system

Answer

The parking brake system

Answer

The anti-lock braking system

Question 5

You are going down a long, steep downgrade and your safe speed is 40 mph. Using the proper braking technique, when and how should you use the service brakes?

Accepted Answer

Brake firmly to about 35 mph, release, and reapply when speed returns to 40 mph — With the vehicle in a proper low gear, apply the brakes just hard enough to feel a definite slowdown; when speed has been reduced to about 5 mph below your safe speed (about 35 mph here), release the brakes. Repeat this cycle each time speed climbs back to your safe speed.

Answer

Hold light, steady brake pressure the whole way down the grade

Answer

Stay off the brakes entirely and rely on the parking brake if needed

Answer

Brake hard to about 20 mph once, then coast the rest of the grade

Question 6

What holds the powerful springs in spring brake chambers back (released) during normal driving?

Accepted Answer

Air pressure — Air pressure holds the springs back during normal driving. If air pressure is lost, the springs put on the brakes — which is why spring brakes work as both parking brakes and emergency brakes.

Answer

Hydraulic fluid pressure

Answer

An electric solenoid

Answer

A mechanical latch set by the driver

Question 7

Air pressure keeps dropping and the spring brakes come on while a heavily loaded vehicle is still moving. Why will it take a long distance to stop?

Accepted Answer

Spring brakes do not act on every axle — Spring brakes are not fitted on all axles, so a heavy load has less braking to stop it once they apply. That is why it is far safer to stop while the tanks still hold enough air for the foot brake.

Answer

The springs take several minutes to apply fully

Answer

The anti-lock system keeps releasing the spring brakes

Answer

The front brake limiting valve cuts spring brake force in half

Question 8

Your straight truck has working anti-lock brakes on every axle, and it is the only kind of vehicle you drive. How may you brake in an emergency stop?

Accepted Answer

You can apply the brakes fully — Normally you use only as much braking force as it takes to come to a safe, controlled stop. The one exception is a driver whose vehicle always has functioning ABS at every axle: that driver may apply the brakes fully to make an emergency stop.

Answer

You must use stab braking, releasing each time the wheels lock

Answer

You should brake lightly and steer onto the shoulder instead

Answer

You should pull the parking brake knob to add the spring brakes

Question 9

When air pressure falls far enough, the spring brakes on tractors and straight trucks come fully on. In what range does that happen?

Accepted Answer

20 to 45 psi — The handbook puts that point between 20 and 45 psi, most often 20 to 30 psi. Don't wait for it: once the low air warning light and buzzer come on, stop safely at once, while the brakes are still under your control.

Answer

55 to 75 psi

Answer

85 to 100 psi

Answer

5 to 10 psi

Question 10

In stab braking, you let off the brakes when the wheels lock. Why must you hold off until the wheels are rolling again before braking hard a second time?

Accepted Answer

If you brake again too soon, the vehicle will not straighten out — Locked wheels can take as long as one second to begin turning again after the brakes are released. Braking again before they roll keeps the vehicle from straightening.

Answer

Braking again too soon overheats the brake drums

Answer

The air compressor needs that time to rebuild pressure

Answer

The spring brakes need that time to release fully

Question 11

You are driving a vehicle with a dual air brake system and one of the two systems loses pressure. What should you expect, and what should you do?

Accepted Answer

Stopping distance increases; stop safely and get the system fixed before driving on — With one system failed, either the front or rear brakes will not fully work, so stopping distance increases. Bring the vehicle to a safe stop and have the system repaired before continuing.

Answer

Braking is unaffected; finish your trip and report it later

Answer

The vehicle cannot be stopped at all; use the escape ramp

Answer

Only the trailer brakes are lost; drive slowly to the destination

Question 12

Some buses have a second control valve, fed by its own air tank, that releases the spring brakes after main air pressure is lost. Why must you plan carefully before using it to move the bus?

Accepted Answer

Its tank holds only enough air to release the brakes a few times — Dual parking control valves let a driver release the spring brakes with air from a separate tank so the vehicle can be moved in an emergency. That supply is small, and without a plan you could end up stopped somewhere dangerous when it is gone.

Answer

Using it permanently disables the spring brakes

Answer

It works only while the engine is shut off

Answer

It releases the brakes on the front axle only

California CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. Your service brakes stop working on a mountain downgrade because they have overheated and faded. What is your best option?

2. What is "controlled braking" in an emergency stop?

3. The low air pressure warning comes on while you are driving. What should you do?

4. Air brakes are really three braking systems in one. Which of them stops the vehicle if the brake system fails, using parts of the other two?

5. You are going down a long, steep downgrade and your safe speed is 40 mph. Using the proper braking technique, when and how should you use the service brakes?

6. What holds the powerful springs in spring brake chambers back (released) during normal driving?

7. Air pressure keeps dropping and the spring brakes come on while a heavily loaded vehicle is still moving. Why will it take a long distance to stop?

8. Your straight truck has working anti-lock brakes on every axle, and it is the only kind of vehicle you drive. How may you brake in an emergency stop?

9. When air pressure falls far enough, the spring brakes on tractors and straight trucks come fully on. In what range does that happen?

10. In stab braking, you let off the brakes when the wheels lock. Why must you hold off until the wheels are rolling again before braking hard a second time?

11. You are driving a vehicle with a dual air brake system and one of the two systems loses pressure. What should you expect, and what should you do?

12. Some buses have a second control valve, fed by its own air tank, that releases the spring brakes after main air pressure is lost. Why must you plan carefully before using it to move the bus?

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