Arizona CDL Permit Test - Combination

You should test the tractor protection valve by allowing the air supply to properly charge, turning off the engine, then releasing air from the system by pressing the brake pedal several times. The tractor protection valve should move into its emergency position when psi drops to an unsafe level.

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.

Before a trip, be sure to inspect all couplings. There should be no space between the upper and lower fifth wheel.

Before coupling together a tractor and a trailer, you should make sure the trailer is at the proper height. If the trailer is too low, the trailer nose may be damaged. If the trailer is too high, it may not be able to couple correctly.

A rollover is more likely if cargo is unevenly loaded in a rig. To help prevent a dangerous rollover, it is important to keep a load as centered on the rig as possible.

To help prevent a rig from rolling over, you should keep the weight of the cargo as close to the ground as possible when loading. You should also drive slowly around turns.

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.