The trailer service air line may also be referred to as the control line or signal line.

When coupling, make sure you couple matching glad hands. They are often color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines.

Before driving a vehicle with a dual air brake system, you should wait for the air compressor to build up at least 100 psi in both the primary and secondary systems.

If you need to make an emergency stop, you can use either the controlled braking method or the stab braking method. It's important to brake in a way that keeps your vehicle traveling in a straight line while still allowing you to turn, if necessary.

A broken exhaust system can let poisonous fumes into a vehicle's cab or sleeper berth. Be sure to inspect your exhaust system for any loose, broken, or missing parts.

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.

Backing is always dangerous because it is impossible to see everything that is behind your vehicle. Only drive in reverse if it is absolutely necessary.

When inspecting the convertor dolly, ensure that all components are present and in proper working condition. Be sure to check the upper and lower fifth wheel, the air lines, and the electric lines. The air lines should be securely attached to the proper glad hands and should not contain any leaks. They should be attached with enough slack to allow easy turning.

Under wet conditions, roads are often most slippery when it first begins to rain. This is because the water mixes with oil and grease on the road that has not yet begun to wash away.

While speaking on a hands-free phone while driving is less dangerous than speaking on a hand-held phone, it is just as likely to mentally distract a driver. Simply engaging in conversation takes their mental focus away from the task of driving.

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.

Some older vehicles with air brakes have front brake limiting valves. These valves were intended to reduce the risk of front wheels skidding. However, research has shown that such devices are unnecessary, so they should be left in the "normal" position.

Double and triple combinations are the most vulnerable to turning over as a result of the "crack-the-whip" effect.

Some pre-1975 vehicles have a front brake limiting valve, which has "normal" and "slippery" settings. The idea behind these valves was to limit the air pressure available to the front brakes when driving on slippery surfaces, and thereby reduce the danger of a front-wheel skid. Studies have found that this is not actually a concern, so if your vehicle has a front brake limiting valve, leave it in the "normal" position.

If steering begins to feel heavy, it is likely that one of your front tires has failed. If you feel a change to your steering, you should exit the road as quickly as is safely possible and check your tires.

It is essential to the safe operation of a CMV that cargo be properly loaded. Improper loading can affect handling and damage the vehicle. Additionally, improperly loaded materials can cause injury or death by falling off of the vehicle.

The combination of slopes and curves can make freeway on- and off-ramps dangerous for trucks. Remember that posted speed limits on ramps may be safe to be driven by cars but too fast to be driven by large or heavily-loaded vehicles.

When backing with a trailer, turn the top of the steering wheel in the direction opposite of where you want to go. Once the trailer begins turning, you should then switch the direction of the steering wheel to follow the trailer.

When backing a truck, always use the mirrors on both sides of the vehicle. Have someone help you whenever possible.

When positioning trailers in a combination, the most heavily-loaded trailer should be the closest to the tractor. The lightest trailer should be positioned in the rear.