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.

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.

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.

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.

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.

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 it is not able to escape from the back of the vehicle.

Landing gear, or trailer supports, should always be completely raised before a vehicle is driven. Landing gear that is not entirely raised could catch on railroad tracks or other hazards on the roadway.

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.

Fully-loaded rigs are more vulnerable to rolling over than empty rigs because the weight of the cargo gives the vehicles higher centers of gravity.

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

If you are unsure of your path while you are driving in reverse, you should stop, exit the vehicle, and recheck your path of travel.

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 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.

Before a trip, ensure that air in the air brake system reaches all trailers. Do this by waiting for air pressure to build, then sending air to both the emergency and service lines and opening the shut-off valves on the rear of the last trailer. If air escapes from the shut-off valves in the rear of the combination, the air is being supplied to the entire vehicle.

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

Incorrect coupling and uncoupling of combination vehicles can have extremely dangerous consequences.

Bobtail tractors are tractors that are not attached to any semitrailers. When operating a bobtail, you should be aware that stopping can be difficult and that it will take a longer distance to come to a complete stop than a tractor attached to a loaded semitrailer.

When coupling, make sure you couple matching glad hands. They are often color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines.