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
Passing Score

15. The trailer hand valve should be used:

Explanation
The trailer hand valve, also called the trolley valve or Johnson bar, is used to work the trailer brakes. It should be used only to test the brakes.

16. If the emergency air line loses pressure:

Explanation
The emergency air line controls the emergency brakes on a combination vehicle. A loss of air pressure in the emergency line will cause the emergency trailer brakes to activate.

17. If color-coded, which color is used to identify emergency, or supply, lines?

Explanation
Air lines are sometimes color-coded to help drivers avoid mistakes when coupling glad hands. Typically, blue is used for service lines and red is used for emergency lines.

18. When backing up your tractor while coupling it to a trailer, the trailer brakes should be:

Explanation
Correctly following the steps to couple and uncouple trailers is vital to safely operating a combination vehicle. Before backing your tractor under the trailer while coupling, make sure your trailer brakes are locked.

19. If you press the tractor air supply control and your trailer's spring brakes do not release, you should:

Explanation
It is important that all of a vehicle's equipment is in proper working condition before beginning a trip. If a trailer's spring brakes do not release when you push in the tractor air supply control, you should make sure the air line connections are properly attached and sealed.

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

Explanation
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.
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