Combination

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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 Drivers License..

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 Drivers 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.

Passing grade:

Before a drive, ensure that air flows to all trailers by:

Explanation
Before a trip, ensure that air in the air brake system reaches all trailers. Do this by waiting for air pressure to build, then sending air to both the emergency and service lines and opening the shut-off valves on the rear of the last trailer. If air escapes from the shut-off valves in the rear of the combination, the air is being supplied to the entire vehicle.

To prevent a rollover, a driver should:

Explanation
Rollovers can happen when a combination vehicle is turned too quickly. To help prevent the risk of rollover, it is important to keep the vehicle's center of gravity low by loading cargo as close to the ground as possible.

What is the Johnson bar?

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.

When driving a trailer with ABS, you should:

Explanation
When driving a tractor-trailer combination equipped with an Anti-Lock Braking System (ABS), you should brake in the same manner that you would if operating a vehicle without ABS.

Large combination vehicles take the longest amount of time to stop:

Explanation
Large combination vehicles take longer to stop when they are empty than when they are loaded. The decreased weight causes a vehicle's wheels to have decreased traction on the surface of the road.

The trailer hand valve should be used:

Explanation
The trailer hand valve should be used only to test the trailer brakes. It should not be used while driving because it may cause the trailer to skid.

Pull out the trailer air supply control 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.
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