Colorado CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

Air pressure has fallen far enough that the spring brakes apply on their own. What hazard does that create for a lightly loaded truck or one on a slick road?

Accepted Answer

The wheels can lock and the vehicle may slide out of control — Spring brakes grab abruptly and cannot be feathered, so with little weight over the tires or poor traction the vehicle can slide and the driver can lose control.

Answer

The air compressor will overheat and shut itself down

Answer

The parking brake knob will push itself back in

Answer

The foot brakes will keep working at full strength

Question 2

On a vehicle with dual parking control valves and a separate air tank, what limits how you use it to move after the main air is lost?

Accepted Answer

The separate tank holds only enough air for a few releases — The separate reservoir holds only enough air to release the spring brakes a few times, so you must plan your move carefully or risk stopping in a bad spot.

Answer

It only works while the engine is off

Answer

It can only be used above 55 mph

Answer

It disables the service brakes while in use

Question 3

You always drive a straight truck whose anti-lock brakes work on every axle. What does the manual allow during an emergency stop?

Accepted Answer

Press the brake pedal all the way down and hold it — A vehicle with functioning anti-lock brakes at every axle is the single exception to modulating pressure: the driver may make a full brake application and let the system prevent lockup.

Answer

Pump the pedal lightly so the system has time to react

Answer

Use stab braking, letting go each time a wheel locks

Answer

Pull the parking brake knob out to help slow the load

Question 4

If the low air pressure warning comes on and pressure keeps falling, why can a heavily loaded vehicle need a long distance to stop?

Accepted Answer

Because the spring brakes do not work on all of the axles — When pressure drops into the 20 to 45 psi range the spring brakes apply, but they do not work on every axle, so a heavy load takes a long distance to stop.

Answer

Because the service brakes get stronger under load

Answer

Because the compressor speeds up under load

Answer

Because ABS shuts off when air is low

Question 5

What causes brakes to fade from excessive heat?

Accepted Answer

Overheating that reduces lining friction and expands the drums — Overusing the service brakes overheats them; the heat changes the lining chemically to reduce friction and expands the drums so the shoes must reach farther with less force.

Answer

Too much moisture drained from the tanks

Answer

Using the engine to help slow the vehicle

Answer

Running the compressor above cut-out pressure

Question 6

How do spring brakes stay released while you are driving?

Accepted Answer

Air pressure holds the springs back until the pressure is removed — Powerful springs are held back by air pressure during normal driving; if that air is removed or lost, the springs apply the brakes.

Answer

A dashboard switch keeps them locked open

Answer

The compressor physically pulls them back

Answer

Engine vacuum holds the springs in place

Question 7

What is the controlled braking method for an emergency stop?

Accepted Answer

Braking as hard as possible without locking the wheels — In controlled braking you apply the brakes as hard as you can without locking the wheels, keeping steering movements small and releasing if the wheels lock.

Answer

Pumping the pedal in a steady rhythm

Answer

Steering hard while releasing all brake pressure

Answer

Locking the wheels and holding them locked

Question 8

On tractors and straight trucks, spring brakes come fully on when air pressure drops into what range?

Accepted Answer

20 to 45 psi — Spring brakes typically apply fully once pressure falls to somewhere in the 20 to 45 psi range (often 20 to 30 psi).

Answer

55 to 70 psi

Answer

80 to 100 psi

Answer

120 to 140 psi

Question 9

Only the trailer of your combination has ABS, and during a hard stop the tractor begins to jackknife. What does the manual tell you to do?

Accepted Answer

Back off the brakes, when it is safe, until you have control again — Easing off the pedal, whenever it is safe to do that, lets the tractor wheels roll again so you can regain steering and straighten the rig.

Answer

Push the pedal down harder to force the tractor straight

Answer

Shift to a lower gear while holding full brake pressure

Answer

Pull the parking brake control to halt the skid

Question 10

What is the purpose of a modulating control valve?

Accepted Answer

It lets you apply the spring brakes gradually if the service brakes fail — A modulating valve lets the driver apply the spring brakes gradually; moving the lever farther applies them harder, which is useful if the service brakes fail.

Answer

It automatically drains the air tanks

Answer

It raises the governor cut-out pressure

Answer

It switches the vehicle from primary to secondary air

Question 11

Which sequence describes the stab braking method?

Accepted Answer

Apply fully, release when the wheels lock, then reapply fully once they roll — In stab braking you apply the brakes fully, release when the wheels lock, and reapply fully once the wheels start rolling again, allowing time for them to roll.

Answer

Hold light steady pressure the whole time

Answer

Steer hard first, then brake once stopped

Answer

Release the brakes and rely on the spring brakes

Question 12

Why can brakes that are out of adjustment leave you without enough braking power to control the vehicle?

Accepted Answer

They quit carrying their share, so the rest overheat and fade — Each brake is supposed to carry part of the work; poorly adjusted ones quit early, so the rest absorb the extra effort, overheat, and fade until braking is no longer adequate.

Answer

They let moisture collect in the tanks and freeze the lines

Answer

They stop the spring brakes from ever releasing

Answer

They make the governor cut out at a much lower pressure

Colorado CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. Air pressure has fallen far enough that the spring brakes apply on their own. What hazard does that create for a lightly loaded truck or one on a slick road?

2. On a vehicle with dual parking control valves and a separate air tank, what limits how you use it to move after the main air is lost?

3. You always drive a straight truck whose anti-lock brakes work on every axle. What does the manual allow during an emergency stop?

4. If the low air pressure warning comes on and pressure keeps falling, why can a heavily loaded vehicle need a long distance to stop?

5. What causes brakes to fade from excessive heat?

6. How do spring brakes stay released while you are driving?

7. What is the controlled braking method for an emergency stop?

8. On tractors and straight trucks, spring brakes come fully on when air pressure drops into what range?

9. Only the trailer of your combination has ABS, and during a hard stop the tractor begins to jackknife. What does the manual tell you to do?

10. What is the purpose of a modulating control valve?

11. Which sequence describes the stab braking method?

12. Why can brakes that are out of adjustment leave you without enough braking power to control the vehicle?

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