Oregon CDL DMV Combination 1

When backing a vehicle with a trailer, you must turn the steering wheel in the direction opposite of where you want to go. Once your trailer starts to turn, you should turn the steering wheel the other way to follow the trailer.

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.

Tractor protection controls in older vehicles may be operated by levers instead of knobs. If an air supply control is set in its "emergency" position, the air supply will be stopped and the trailer emergency brakes will be applied.

Because the weight of cargo gives them a higher center of gravity, fully-loaded rigs are 10 times more likely to roll over in a crash than empty rigs.

Due to the "crack-the-whip" effect caused by rearward amplification, changing lanes too quickly in a combination vehicle can result in a rollover.

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.

When driving a vehicle with ABS, you should brake in the same manner as you would in a vehicle without ABS.

Making a sudden lane change can be dangerous while driving a combination vehicle. You can avoid the need to make a sudden lange change by looking down the road for upcoming obstacles that will require you to change lanes.

Double and triple combinations are the most vulnerable to turning over as a result of the "crack-the-whip" effect.

The "crack-the-whip" effect can cause a trailer to turn over during a lane change. To avoid this phenomenon, drivers should make lane changes at slow, safe speeds.

To reduce the risk of a rollover, the weight of cargo in a trailer should be kept as low to the ground as possible. Weight should not be placed primarily on one side of the trailer as this could make the trailer lean, increasing the risk of a rollover.

Driving combination vehicles requires more skill than driving single commercial vehicles. Combinations are generally longer, generally heavier, and are more vulnerable to rollover.

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.

The service line, also called the control line or signal line, carries air to the trailer brakes and is controlled by the foot brake or trailer hand brake.

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.

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.

The emergency air line controls the emergency brakes on a combination vehicle. A loss of air pressure in the emergency line will cause the emergency trailer brakes to activate.

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.

When starting a trip, be sure that all shut-off valves are in the open position, except for the last valves on the rear trailer. It is important that air reaches the brakes on all trailers and that the air is not able to escape from the back of the vehicle.

The trailer hand valve works the trailer brakes but should only be used when testing them. Using it while driving could create a skid. Never use the trailer hand valve while parking because doing so may release the air pressure from the braking system, releasing the brakes that are holding the vehicle in place.