The service line, also called the control line or signal line, carries air to the trailer brakes and is controlled by the foot brake or trailer hand brake.

To reduce the chances of driving distracted, you should avoid eating, drinking, or smoking while driving. Anything that diverts attention from the task of driving is a distraction.

Railroad-highway crossings may be difficult to cross if you are pulling a trailer with low underneath clearance. In particular, both low-slung units and single-axle tractors pulling long trailers are especially challenging to drive over raised crossings.

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.

Cargo needs to be secured appropriately to prevent it from moving in transit. Cargo should be arranged to keep the vehicle's center of gravity low and well-distributed.

A trailer tends to swing around, potentially resulting in a trailer jackknife, if its wheels lock up.

Anti-Lock Braking System (ABS) malfunction lamps are usually yellow. Even if the ABS isn't working properly, a driver will still have access to the vehicle's usual braking functions.

After a vehicle is started, the warning lights and buzzers should go out after a few seconds. If the warning signals do not turn off, there may be something wrong with the vehicle.

It is important to know the maximum air loss rate that is safe for your specific vehicle. A triple combination should have a leakage rate no higher than 6 psi in a minute during an applied leakage test.

Placards must be placed on the outside of vehicles carrying hazardous materials. They identify the specific class or classes of materials being carried and warn others of relevant hazards.

When operating a double or triple, the shut-off valves at the rear of the last trailer should be closed. All other shut-off valves should be open.

Prescription and over-the-counter medications may have side effects that can impair a person's ability to drive safely. It is illegal to operate a motor vehicle while under the influence of alcohol or any other controlled substance, including some over-the-counter medications.

Rollovers happen when a vehicle is driven too fast. To reduce the risk of rollover, make sure the weight of cargo is loaded low to the ground, and that you take turns and curves slowly.

Never unlock the pintle hook with the dolly still under the rear trailer. This could cause the dolly tow bar to fly up, possibly causing serious injury.

Compressed air in an air brake system usually contains a certain amount of water and compressor oil. The water and oil can damage the brakes if left to accumulate in the system. Tanks must be drained regularly to remove this build-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.

Backing up is always dangerous because it is impossible to see everything behind your vehicle. If you must drive in reverse, use a helper, if possible.

Be especially cautious when driving on ice that has begun to melt. Ice that is wet is much more slippery than ice that is dry.

If you use the parking brakes when the weather is very wet and the temperature is below freezing, the brakes may become frozen, preventing the vehicle from moving.

There are seven basic steps to a pre-trip inspection. These steps include completing an overview of the vehicle; checking the engine compartment; starting the engine and inspecting inside the cab; turning off the engine and checking the lights; a walk-around inspection; checking the signal lights; and starting the engine and checking the brakes.