Oklahoma CDL Permit Test - Double

Roads are particularly slippery when it first begins to rain. The water mixes with oil drippings on the road that have not yet washed away, creating a slippery and dangerous mixture.

When positioning trailers in a combination, the most heavily-loaded trailer should be the closest to the tractor. The lightest trailer should be positioned in the rear.

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. Using it while a vehicle is in motion could cause a skid.

Be sure to check your mirrors before beginning a drive. Your posture may change day to day and your mirrors may need to be adjusted.

When coupling air brake hoses, you should make sure the proper pairs of gland hands are connected. They are sometimes color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines.

Landing gear, or trailer supports, should always be completely raised before a vehicle is driven. When uncoupling, landing gear should be lowered to make firm contact with the ground. If a trailer is loaded when it is being uncoupled, you should lower the landing gear and turn the crank a few additional times to remove some weight from the trailer.

If your trailer begins to drift while you are backing, you should correct the drift immediately by turning the top of the steering wheel in the direction of the drift.