North Carolina CDL DMV Combination 1

More than half of all accident-related truck driver deaths are a result of truck rollovers. To help prevent a rollover, be sure to load cargo low to the ground and centered on your rig. Take corners slowly and carefully.

In general, the parts of the service air line are coded blue and the parts of the emergency air line are coded red.

Tractor protection controls in older vehicles may be operated by levers instead of knobs. If an air supply control is set in its "normal" position, it is properly set for you to pull a trailer.

Trailers and converter dollies manufactured on or after March 1, 1998 are required to have Anti-Lock Braking Systems (ABS).

Older trailers do not have spring brakes. This means that if the air supply in an older trailer's air tank has leaked away, there will be no working brakes connected to the trailer and its wheels will turn freely.

Triple combination trailers are most vulnerable to the "crack-the-whip" effect.

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.

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.

The tractor protection valve keeps air in the trailer's braking system should the trailer break away or develop a leak. A loss of air pressure in the emergency line will cause the tractor protection valve to open and the emergency trailer brakes to activate.

It is important that all of your vehicle's equipment is in proper working condition before you begin a trip. If a trailer's spring brakes do not release when you push in the tractor air supply control, you should make sure the air line connections are properly attached and sealed.

Combination vehicles require more space on the road than other vehicles. When entering or crossing traffic while driving a combination vehicle, it is especially important that there is a large enough gap in traffic for you to safely do so.

An empty trailer will require a longer stopping distance than a loaded trailer. Additionally, a trailer is most likely to swing out and strike other vehicles when it is lightly loaded or empty.

Never use the trailer hand valve while operating your vehicle. Using the trailer hand valve while driving can cause your trailer to skid.

The trailer hand valve should not be used for parking. This could cause all of the air to leak out of the braking system, resulting in the brakes releasing. Instead, use the parking brake.

Combination vehicles need more space on the road than other commercial vehicles because they are longer and need more space to turn and stop. It is especially important to properly manage space when you are operating a combination vehicle.

In vehicles equipped with an automatic tractor protection valve, the valve will pop out if air pressure drops to a level between 20 and 45 psi. When the valve pops out, the protection valve will close, stopping the flow of air.

Trailers and converter dollies built on or after March 1, 1998 are required to have Anti-Lock Braking Systems (ABS). This will be indicated by the presence of a yellow malfunction lamp. You can determine if older trailers have ABS by checking under the trailers for ECU and wheel speed sensor wires coming from the back of the brakes.

A trailer tends to swing around, potentially resulting in a trailer jackknife, if its wheels lock up.

All trailers and converter dollies manufactured on or after March 1, 1998 must have Anti-Lock Braking Systems (ABS).

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.

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.

When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is known as off-tracking, or "cheating."

The emergency air line (also known as the supply line) has two functions. The first is to supply air to the trailer air tanks on a combination vehicle, and the second is to control the emergency brakes.

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.

When coupling, be sure to couple the proper glad hands. When glad hands are connected, the seals should be pressed together at a 90-degree angle.