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 Maryland 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 and true/false 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

15. A trolley valve:

Should be used while driving.

Should only be used to test trailer brakes.

Should be used when parking uphill.

The trailer hand valve (also referred to as the trolley valve or Johnson bar) is a mechanism that works the trailer brakes. It should only be used to test the brakes. Using it while the vehicle is being driven could cause a skid. Never use the trailer hand valve while parking because doing so may release the air pressure from the braking system, releasing the brakes that are holding the vehicle in place.

16. To find out if a vehicle that was built before 1998 has an Anti-Lock Braking System (ABS), you can:

Pump the air brakes to activate the ABS.

Look into the back of the fifth wheel.

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

If you are operating a vehicle built before 1998 and are unsure if the trailer has an Anti-Lock Braking System (ABS), you can check under the trailer for wheel speed sensors coming from the back of the brakes.

17. If a load is placed on one side of a trailer, the trailer:

May lean, and could result in a rollover.

May add extra support during turns.

Have improved braking.

Have improved steering.

If the weight of a load is placed primarily one side of a trailer, the trailer may lean, increasing the risk of a rollover.

18. The best way to recognize that your trailer has started to skid is by:

Seeing other drivers' faces.

Checking the trailer in your mirrors.

Feeling the trailer move.

The easiest way to become aware that your trailer has begun to jackknife is to observe it in your mirrors. Checking your trailer in your mirrors will also allow you to spot any skidding at the earliest possible moment.

19. After connecting the air lines to the trailer while coupling, you should:

Supply air to the trailer.

Chock the wheels.

Inspect the fifth wheel.

Connect the electrical cord.

Correctly following the steps to couple and uncouple trailers is vital to safely operating a combination vehicle. After connecting the air lines to the trailer while coupling, you should supply air to the trailer.

20. The trailer hand valve:

Should always be used for parking.

Should only be used for parking on a downgrade.

Should never be used for parking.

Never use the trailer hand valve while parking because doing so may release the air pressure from the braking system, releasing the brakes that are holding the vehicle in place. Instead, use the parking brake or wheel chocks.

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