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

Placards are diamond-shaped warning signs that are placed on the outside of vehicles carrying hazardous materials. Placards are used to identify the specific hazard classes of the cargo being carried.

It is safest not to drive in foggy areas. However, if you must drive through fog, you should slow down, use your low beam headlights and fog lights, and turn on your four-way flashers.

ABS increases a driver's control during braking. It will not necessarily change the distance needed for a vehicle to come to a complete stop.

If you are attaching a second trailer to a combination but you have doubts about the trailer's brakes, you should use wheel chocks to secure the trailer in place while coupling.

Brakes heat up with use. If they are overused and become too hot, expansion and chemical changes will make them less effective and eventually cause them to stop working altogether. This is known as "brake fade."

When uncoupling a triple trailer rig, it is important to uncouple the third trailer first. Uncouple the remaining trailers as you would normally uncouple a double.

Rust around wheel nuts can indicate that they are loose. If you observe rust, check the tightness of the nuts.

The suspension system is responsible for supporting a vehicle, supporting its load, and keeping its axles in place. When inspecting your vehicle, check for damaged or missing spring hangers, spring leaves, shock absorbers, u-bolts, and frame members. Broken parts in the suspension system are extremely dangerous.

Because air expands when hot, tire pressure increases as temperatures increase. This can sometimes result in tire failure. Consistently check your tire pressure when making a trip in hot weather.

If you are approaching a traffic light that has been green for a long time, there is a good chance that it will turn yellow before you reach it. Start slowing down and be ready to stop.

In general, the parts of the service air line are coded blue and the parts of the emergency air line are coded red.

If a pre-trip inspection reveals anything unsafe about your vehicle, you must get it repaired. It is illegal to operate an unsafe vehicle.

If you must drive in fog, you should use your low beam headlights and fog lights, even during the daytime.

The driver of a double or triple combination must be especially conscious of the space surrounding their vehicle. Doubles and triples need more room to turn and stop than other smaller vehicles.

Air tanks should be drained daily to remove water and oil buildup. An excess of oil and water in the air tanks can interfere with proper brake function.

During an inspection, there are a number of tire problems to check for and avoid. Look for air pressure that is too low or too high; excessive wear; cuts or other damage; tread separation; dual tires that come into contact with each other or other parts of the vehicle; mismatched tire sizes; radial and bias-ply tires used together; cut or cracked valve stems; and regrooved, recapped, or retreaded tires on the front wheels of a school bus.

To correct a drive-wheel braking skid, you should first remove your foot from the brake pedal to allow the locked wheels to begin rolling again. Quickly steer in the direction you want to go, then countersteer to prevent your vehicle from skidding in the opposite direction.

It is essential that drivers of doubles and triples are able to correctly couple and uncouple their trailers. Improperly coupling and uncoupling trailers is extremely dangerous.

In extremely hot weather, tire pressure can increase to dangerous levels due to the expansion of the air in heat. To keep an engine from overheating, it is important that there be enough oil and coolant in the engine compartment.