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.

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.

If your trailer goes off course while you are backing, you should pull your truck forward and reposition your vehicle as needed before continuing to back up.

In a combination vehicle with air brakes, the tractor protection valve keeps air in the tractor or truck brake system in the event of the trailer breaking away or developing a leak.

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.

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.

Air pressure in the service air line is controlled by either the foot brake or trailer hand brake. The service air line is also known as the control line or signal line. This line is connected to relay valves, which allow the trailer brakes to be applied more quickly than would otherwise be possible.

Failure to keep the fifth wheel plate properly lubricated can create friction between the tractor and trailer, causing steering problems.

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.

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.

The earliest and best way to recognize the beginnings of a trailer skid is by seeing the trailer veer off-course in your mirrors.

The service air line carries air and is controlled by either the foot brake or trailer hand brake. The service air line is attached to relay valves, which allow the trailer brakes to be applied quickly.

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.

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.

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.

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

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

Shut-off valves are used in air supply lines to control the passage of air from one trailer to another. The rear shut-off valve should always be closed to prevent air from leaving the braking system.

Before a trip, you should ensure that air reaches all air brakes on all trailers by opening up the rear emergency line and service line shut-off valves to listen for escaping air. Close both shut-off valves before beginning to drive.