Instructions

Combination

All applicants who are applying for a Class A CDL should be prepared to take the Combination test. This test covers information found in Section 6 of the Commercial Driver License.. Read More

All applicants who are applying for a Class A CDL should be prepared to take the Combination test. This test covers information found in Section 6 of the Commercial Driver License Manual. Section 6 provides the information needed to safely operate tractor-trailers, doubles, triples, and straight trucks with trailers. The test is made up of 20 multiple-choice questions, and applicants will need to correctly answer a minimum of 16 questions to pass. The Combination test is not a replacement for the Double/Triple endorsement test.

Number of Question 20

Passing Score 16

8. What is another name for the service line?

The control line

The utility line

The open line

The parallel line

The trailer service air line may also be referred to as the control line or signal line.

9. What does the tractor protection valve do?

Protects the tractor from being stolen

Protects the tractor from exceeding a set speed

Keeps air in the braking system, should the trailer break away or develop a leak

Ensures oil adequately lubricates the engine

The tractor protection valve keeps air in the tractor or truck braking system, should the trailer break away or develop a bad leak.

10. If the trailer begins to skid, it is best to:

Release the brakes.

Accelerate.

Quickly turn the steering wheel one way, then the other.

Brake.

If your trailer begins to skid, you should release the brakes to help regain traction. Once the wheels grip the road again, the trailer will begin to straighten out and follow the path of the tractor.

11. To prevent a trailer from rolling over, you should:

Speed up when nearing a corner.

Make sudden steering moves.

Take on-ramps faster than the posted speed limit.

Drive slowly around corners.

To reduce the risk of a rollover when driving a combination vehicle, you should keep the weight of the cargo as low to the ground as possible and drive slowly around turns.

12. If a trailer begins to jackknife, you should not:

Release the brakes.

Apply the trailer hand brake.

Allow the wheels to grip the road.

Allow the trailer to straighten out.

If a trailer begins to jackknife, you should release the brakes and allow the trailer wheels to regain traction with the road. Do not apply the trailer hand brake to attempt to straighten out the rig because it will only prolong the skid. The application of brakes is what caused the wheels to lock in the first place.

13. If unsure if a trailer is equipped with ABS, you can:

Check under the trailer for wheel speed sensors coming from the back of the brakes.

Try driving on a slippery surface and see if ABS kicks in.

Assume it does have ABS.

Remove a tire and look for the ABS sensor on the axle.

Trailers and converter dollies built on or after March 1, 1998 are required to have Anti-Lock Braking Systems (ABS). This will be indicated by the presence of a yellow malfunction lamp. You can determine if older trailers have ABS by checking under the trailers for ECU and wheel speed sensor wires coming from the back of the brakes.

14. In a vehicle equipped with an automatic tractor protection valve, the valve will pop out when:

Air pressure drops to a level between 20 and 45 psi.

You are experiencing a trailer jackknife.

Wheels have regained traction after a skid.

Air pressure is above 45 psi.

In vehicles equipped with an automatic tractor protection valve, the valve will pop out if air pressure drops to a level between 20 and 45 psi. When the valve pops out, the protection valve will close, stopping the flow of air.

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