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

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

Explanation
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.

9. When backing a trailer, how should you turn the steering wheel?

Explanation
When backing with a trailer, turn the top of the steering wheel in the direction opposite of where you want to go. Once the trailer begins turning, you should then switch the direction of the steering wheel to follow the trailer.

10. In a vehicle equipped with an automatic tractor protection valve, the valve will pop out when air pressure drops to a level between:

Explanation
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.

11. Place the trailer air supply control in its "emergency" position to test:

Explanation
Be sure to test the trailer emergency brakes before beginning a trip. After ensuring that the trailer rolls freely, you can test the emergency brakes by pulling out the trailer air supply control, or placing it in the "emergency" position. Pull forward slightly with the tractor and make sure the trailer does not move.

12. Which type of vehicle is most prone to the “crack-the-whip” effect?

Explanation
Triple combination trailers are most vulnerable to the "crack-the-whip" effect.

13. Rollovers happen when:

Explanation
Rollovers are caused by operators turning too fast. To avoid rolling over, drive slowly on entrance ramps, on exit ramps, and around corners. Avoid making quick lane changes when towing trailers.

14. What is another name for the service line?

Explanation
The service line, also called the control line or signal line, carries air to the trailer brakes and is controlled by the foot brake or trailer hand brake.
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