Nebraska CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

Some vehicles, buses among them, carry a separate air tank tied to the parking brake controls. What is it there for?

Accepted Answer

To release the spring brakes so the vehicle can be moved in an emergency after main air pressure is lost — Losing main air pressure brings the spring brakes on. On vehicles with dual parking control valves, pushing in the spring-loaded control sends air from a separate tank to release the spring brakes so the vehicle can be moved in an emergency. That tank holds enough air for only a few such releases.

Answer

To give the service brakes extra stopping power on downgrades

Answer

To keep the low air warning from sounding in traffic

Answer

To hold the spring brakes off for good once air is lost

Question 2

You are driving a truck with a dual air system. The secondary gauge is sinking toward 55 psi while the primary still reads normal. What should happen, and what should you do?

Accepted Answer

The low air warning should activate, and you should stop right away and park safely — In a dual system the light and buzzer are supposed to activate before either system falls below 55 psi; they do not wait for both. If that happens on the road, the manual says to stop immediately and park the vehicle safely. With one system very low, the front or the rear brakes are not working fully, so stopping takes longer.

Answer

Nothing happens until both systems are below 55 psi, so keep driving

Answer

The spring brakes apply at once, so brace for a sudden stop

Answer

The governor shifts air over from the primary side, so no action is needed

Question 3

Using controlled braking, you had to release the brakes because the wheels locked. When does the manual say to put them back on?

Accepted Answer

As soon as you can — In controlled braking you release the brakes if the wheels lock or if a bigger steering correction is needed. The manual says to get back on the brakes as soon as you can.

Answer

After a full three seconds

Answer

Only after the vehicle has stopped rolling

Answer

Not until you have shifted to a lower gear

Question 4

If the low pressure warning signal does not work, you could lose air without knowing it. Which pairing of system type and result matches the manual?

Accepted Answer

Single-circuit system – sudden emergency braking; dual system – longer stopping distance — The manual says an unnoticed loss of air could trigger sudden emergency braking where the system is single-circuit. In a dual system the stopping distance grows, and only limited braking is left before the spring brakes apply.

Answer

Single-circuit system – longer stopping distance; dual system – sudden emergency braking

Answer

Single-circuit system – no effect; dual system – total loss of brakes

Answer

Either system – the governor shuts the engine down

Question 5

Your low air pressure warning comes on while you are driving. The manual tells you to stop and park safely as soon as possible. What does it suggest might be wrong?

Accepted Answer

The system may have an air leak — A low air warning may mean air is leaking from the system. Controlled braking works only while the tanks still hold enough air, so stopping early, while the foot brakes still work, beats waiting for the spring brakes to come on.

Answer

The brakes are probably too cold

Answer

The alcohol evaporator is likely empty

Answer

The governor has probably cut out early

Question 6

The manual says you may or may not stop faster with ABS. What does it say ABS should still let you do during a hard stop?

Accepted Answer

Keep steering, so you can go around an obstacle, and avoid a skid from braking too hard — ABS senses a wheel that is about to lock and lowers the braking pressure. With the wheels kept from locking, the driver should still be able to steer past an obstacle while braking, and skids from overbraking are avoided.

Answer

Lock the wheels on purpose to shorten the stop

Answer

Follow the vehicle ahead more closely

Answer

Use the parking brake to help slow the vehicle

Question 7

What form does the manual say the low air pressure warning usually takes?

Accepted Answer

A red light, which may be joined by a buzzer — A low air pressure warning that the driver can see is required, and it has to activate before the tanks fall below 55 psi. The manual says it is usually a red light and that a buzzer may sound too.

Answer

A yellow light on the instrument panel

Answer

A green light that goes dark when pressure is low

Answer

A chime with no light at all

Question 8

In an emergency, a driver applies the brakes all the way, lets off when the wheels lock, and applies them fully again once the wheels are rolling. Which method is this?

Accepted Answer

Stab braking — Stab braking is full application, release at lockup, and full application again once the wheels roll. Controlled braking, the other method the manual gives, keeps the brakes just short of locking the wheels.

Answer

Controlled braking

Answer

Modulated braking

Answer

Engine braking

Question 9

A truck's low air warning is a 'wig wag.' What does that device do when system pressure falls below 55 psi?

Accepted Answer

It drops a mechanical arm into the driver's view — A wig wag is a mechanical low air warning. When system pressure goes under 55 psi, an arm swings down where the driver can see it. Automatic versions lift back out of sight once pressure recovers; manual reset versions must be put back by hand.

Answer

It sounds the horn in short bursts

Answer

It flashes the brake lights to warn traffic behind

Answer

It vents the tanks through the safety valve

Question 10

While you are braking with the controlled braking method, how much should you move the steering wheel?

Accepted Answer

Very little; keep steering movements very small — Controlled braking means braking as hard as possible short of wheel lockup while keeping steering movements very small. If a bigger steering correction is needed, or the wheels lock, you release the brakes and then reapply as soon as possible.

Answer

As much as you like, since the wheels cannot lock

Answer

Not at all; hold the wheel rigidly straight ahead

Answer

In quick left-right motions to scrub off speed

Question 11

If a driver keeps overusing brakes that are already fading, where does the manual say this can end?

Accepted Answer

The vehicle can no longer be slowed or stopped — Overusing the service brakes overheats them and leads to fade. The manual warns that continued overuse can deepen the fade to the point where slowing or stopping the vehicle is no longer possible.

Answer

The spring brakes apply and stop the vehicle safely

Answer

The ABS takes over and restores full braking

Answer

The governor cuts in and cools the drums

Nebraska CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. Some vehicles, buses among them, carry a separate air tank tied to the parking brake controls. What is it there for?

2. You are driving a truck with a dual air system. The secondary gauge is sinking toward 55 psi while the primary still reads normal. What should happen, and what should you do?

3. Using controlled braking, you had to release the brakes because the wheels locked. When does the manual say to put them back on?

4. If the low pressure warning signal does not work, you could lose air without knowing it. Which pairing of system type and result matches the manual?

5. Your low air pressure warning comes on while you are driving. The manual tells you to stop and park safely as soon as possible. What does it suggest might be wrong?

6. The manual says you may or may not stop faster with ABS. What does it say ABS should still let you do during a hard stop?

7. What form does the manual say the low air pressure warning usually takes?

8. In an emergency, a driver applies the brakes all the way, lets off when the wheels lock, and applies them fully again once the wheels are rolling. Which method is this?

9. A truck's low air warning is a 'wig wag.' What does that device do when system pressure falls below 55 psi?

10. While you are braking with the controlled braking method, how much should you move the steering wheel?

11. If a driver keeps overusing brakes that are already fading, where does the manual say this can end?

More CDL — Air Brakes topics

Practice Handling Emergencies in another state