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 a vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is called off-tracking. This effect is especially pronounced on vehicles with trailers.

The trailer hand valve should be used only to test the trailer brakes. It should not be used while driving because it may cause the trailer to skid.

While inspecting a coupling, you should go under the trailer and look into the back of the fifth wheel. Ensure that the fifth wheel jaws are secured around the shank of the kingpin.

When driving a combination vehicle, it is important to brake well in advance and look far ahead of your vehicle to avoid the need for sudden stops. Making habits of these actions will help you prevent your trailer from jackknifing.

Trailers can overturn as a result of the "crack-the-whip" effect. The last trailer in a combination is the most prone to tip over due to this effect. Drivers should be aware of the rearward amplification of their specific vehicles and drive accordingly.

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.

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.

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.

A trailer may swing out and strike other vehicles if its wheels lock up. This is especially likely with lightly-loaded trailers.

The easiest way to spot a trailer skid is to use your mirrors. Any time you brake hard, check your mirrors to ensure that your trailer is still in its proper position.

When driving a tractor-trailer combination equipped with an Anti-Lock Braking System (ABS), you should brake in the same manner that you would in a vehicle without ABS.

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.

When any vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is called off-tracking. The degree of off-tracking will be greater on long vehicles than on short vehicles.

The trailer hand valve (also referred to as the trolley valve or Johnson bar) is a mechanism that works the trailer brakes. It should only be used to test the brakes. Using it while the vehicle is being driven could cause 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.

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 the weight of a load is placed primarily one side of a trailer, the trailer may lean, increasing the risk of a rollover.

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.

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.

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. Instead, use the parking brake or wheel chocks.