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

Distractions that can affect safe driving can be classified as physical (such as reaching for an object), mental (such as talking with passenger), or both (such as talking on a hand-held phone).

Rollovers can happen when a combination vehicle is turned too quickly. To help prevent the risk of rollover, it is important to keep the vehicle's center of gravity low by loading cargo as close to the ground as possible.

Before a trip, be sure to inspect all couplings. There should be no space between the upper and lower fifth wheel.

Always downshift before beginning to drive downhill. Forcing an automatic transmission into a lower gear at a high speed could damage the transmission and also lead to a loss of ability to engine brake. Drive at a speed that will allow you to control your vehicle without overusing your brakes. When determining a safe speed to drive, you should take into account the steepness of the grade, the length of the grade, the weight of your vehicle, road conditions, and weather conditions.

In general, vehicles carrying hazardous materials are required to display diamond-shaped warning signs on all four sides. These warning signs are called "placards."

The service air line carries air and is controlled by either the foot brake or trailer hand brake. The service air line is attached to relay valves, which allow the trailer brakes to be applied quickly.

On many vehicles, multi-speed rear axles and auxiliary transmissions are used to provide extra gears. They are usually controlled by a selector knob on the gearshift lever.

The average driver has a reaction time between three-quarters of a second and one second. At 55 mph, this corresponds to a distance of 61 feet traveled.

When inspecting any kind of tank, it is most important to check the tank for leaks. It is illegal to transport any gas or liquid in a leaking tank.

The securement of cargo must be checked before beginning a trip, within the first 50 miles of a trip, and then again every three hours or 150 miles.

Stopping is not always the safest response to a hazard on the road. You can almost always turn to avoid an obstacle faster than you can stop.

Combination vehicles are usually heavier and longer than single commercial vehicles. For these reasons, they usually require more driving skill than single commercial vehicles.

To reduce the risk of a rollover, the weight of cargo in a trailer should be kept as low to the ground as possible. Weight should not be placed primarily on one side of the trailer as this could make the trailer lean, increasing the risk of a rollover.

Press the brake pedal down smoothly and gradually every time you slow or stop. The amount of brake pressure you need to apply depends on the speed of your vehicle and how quickly you need to stop.

Black ice is a thin layer of ice that is clear enough for the road surface to be seen through it. A road covered in black ice may look like it is merely wet. You should be very careful when temperatures are below freezing and the road looks wet.

Smoking, eating, or drinking are distracting activities and should be avoided while you are driving. Instead, plan ahead and allow yourself time to stop to eat when making a lengthy trip.

Tank vehicles carrying liquid cargo are vulnerable to surge. Liquid surge is an occurrence in which a wave of liquid sloshes from one end or side of a tank to the other, causing dangerous effects on handling.

Once you have begun to drive after a tire has been changed, you should stop after a short distance to recheck the tightness of the lug nuts.

If a cargo of hazardous materials begins to leak, do not move your vehicle any more than safety requires. If you continue to drive, an even larger area will become contaminated. Instead, you should park your vehicle, secure it, stay with the vehicle, and contact the proper emergency personnel. If you do not have access to a phone, you should send someone else to get help.