The trailer hand valve (also referred to as the "trolley valve" or "Johnson bar") works the trailer brakes and should be used only when testing them. Using the trailer hand valve while driving could result in a skid.

To check the connection between the trailer and tractor.

Vehicles with trailers are vulnerable to rollover due to the "crack-the-whip" effect, which is caused by rearward amplification.

The cause of the "crack-the-whip" effect.

The amount of noise projected to the rear of a vehicle.

The cause of the "crack-the-whip" effect.

The number of trailers that can be pulled by a tractor.

Push in the trailer air supply control to supply the trailer with air. Pull out the trailer air supply control to turn off the air supply and activate the emergency brakes.

Prevent the vehicle from skidding.

If your trailer begins to skid, you should release the brakes to regain traction. The trailer will begin to straighten out once the wheels begin to grip the road again.

Quickly turn the steering wheel in one direction, then in the other.

The "crack-the-whip" effect is a result of rearward amplification. If not properly handled, a trailer can tip over due to rearward amplification.

The cause of the "crack-the-whip" effect.

The amount of noise projected to the rear of the vehicle.

The cause of the "crack-the-whip" effect.

The number of trailers that can be pulled by one tractor.

Combination Vehicles Practice Test | Idaho 2024 #2 Page 3 of 3

Train for FREE online with our Idaho CDL combination vehicle test. The official exam test consists of several obligatory parts, with all of them checking your knowledge of different blocks of road rules. If you need to obtain a ID combination license in 2024, practice as much as possible. Free sample tests published on our website will help you check and improve your knowledge and boost your grades. Please bear in mind that DMV requirements for issuing a combination license may vary from state to state.

Number of Question 20

Passing Score 16

Number of Tests 20

Combination Vehicles Practice Test | Idaho 2024 #2 Page 3 of 3

15 . The service air line is often controlled by the foot brake and is attached to the ____ valves.

16 . The trailer hand valve should be used:

17 . Rearward amplification refers to:

18 . Pushing in the trailer air supply control will:

19 . If a trailer begins to skid, it is best for the driver to:

20 . Rearward amplification refers to:

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