Trailers built before 1975 are not required to have spring brakes. When parking a trailer without spring brakes, be sure to use wheel chocks to prevent the trailer from rolling.

If you do not know whether or not a trailer is equipped with ABS, look under the vehicle for the electronic control unit and wheel speed sensor wires coming from the back of the brakes.

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.

Vehicles with trailers are vulnerable to rollover due to the "crack-the-whip" effect, which is caused by rearward amplification.

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

To reduce the risk of tipping over when driving with a trailer, you should steer gently and smoothly. Avoid making sudden movements.

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.

If a parked trailer does not have spring brakes, wheel chocks should be used to prevent it from moving.

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

A tractor protection valve keeps air in a tractor or truck air brake system should the trailer break away or develop a bad leak. The valve will close automatically if the pressure drops to an unsafe level.

You should always steer gently and smoothly while pulling a trailer. Making sudden steering moves could cause the trailer to tip over.

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.

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 enonugh gap in traffic to safely do so.

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

To test the trailer service brakes, you should first ensure that the braking system has a normal air pressure level, then release the parking brake. You should then move the vehicle forward slowly and apply the brakes with the hand control. If the trailer service brakes are working properly, you will feel the brakes activate.

When making a turn, be sure to steer gently and smoothly. Making a quick turn while pulling trailers is dangerous and can increase the risk of the last trailer rolling over.

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.

When backing a vehicle without a trailer, a driver must turn the vehicle in the direction that they want to go. However, when backing with a trailer, the driver must begin by turning in the opposite direction. Once the trailer starts to turn, they should turn the wheel in the other direction to follow the trailer.

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