Tractors without semi-trailers are referred to as "bobtail tractors." Bobtail tractors are difficult to operate and drivers must exercise caution.

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.

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.

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.

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.

When driving a tractor-trailer combination that is equipped with an Anti-Lock Braking System (ABS), you should brake in the same manner that you would if the vehicle was not equipped with ABS.

When coupling, be sure to couple the proper glad hands. When glad hands are connected, the seals should be pressed together at a 90-degree angle.

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.

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.

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.

Combination vehicles are usually heavier and longer than single combination vehicles. Operating a combination vehicle requires a higher level of driving skill than operating a single commercial vehicle.

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.

If a vehicle has anti-lock brakes on just one axle, the driver will still have more control during braking than they would without any anti-lock brakes.

Older trailers do not have spring brakes. This means that if the air supply in an older trailer's air tank has leaked away, there will be no working brakes connected to the trailer and its wheels will turn freely.

Never use the trailer hand valve while operating your vehicle. Using the trailer hand valve while driving can cause your trailer to skid.

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.

Air lines are sometimes color-coded to help drivers avoid mistakes when coupling glad hands. Typically, blue is used for service lines and red is used for emergency lines.

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.

The "crack-the-whip" effect is a result of rearward amplification. If not properly handled, a trailer can tip over due to rearward amplification.