Double and triple trailers are less stable than single commercial vehicles and are more likely to roll over when being driven. To prevent rollovers, doubles and triples must be driven very smoothly and gently.

If a federal or state inspector judges a CMV to be unsafe, they may put it out-of-service until it is fixed.

Always turn on your four-way emergency flashers if you must park on the side of the road. This is especially important when traveling at night.

If your hydraulic bakes fail, shifting into a lower gear can help slow your vehicle down.

When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is known as off-tracking, or "cheating."

If you are fatigued, you will not see or react to hazards as quickly as you would if you were fully energized and awake. You will be impaired in making critical decisions.

The majority of heavy-duty vehicles are equipped with dual air brake systems.

In an air brake system, there are three different braking systems: a service brake system, a parking brake system, and an emergency brake system. The emergency brake system uses parts of both the parking and service brake systems.

When performing a visual check of coupling devices, you should make sure there is no space between the upper and lower fifth wheel. Ensure that the locking jaws are securely closed around the shank of the kingpin.

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.

If the weight of a load is poorly balanced, it can lead to difficult and unsafe handling of a vehicle.

Before a trip, ensure that air in the air brake system reaches all trailers. Do this by waiting for air pressure to build, then sending air to both the emergency and service lines and opening the shut-off valves on the rear of the last trailer. If air escapes from the shut-off valves at the rear of the combination, the air is being supplied to the entire vehicle.

You should not apply the brake pedal if the spring brakes are activated. The brakes could be damaged if they are subjected to the force of air pressure and the springs at the same time.

Check each slack adjuster after parking on level ground, setting wheel chocks, and disengaging the parking brake. Pull the slack adjusters to make sure they do not move more than about one inch from where the push rod is attached. If they move more than one inch, they may be out of adjustment and will need to be fixed.

Before inspecting the engine compartment, make sure that the parking brakes are on and/or the wheels are chocked. Check the engine compartment before entering the cab and starting the engine.

In vehicles with air brakes, the parking brake is controlled by a knob. The knob is pulled out to apply the brakes, and pushed in to release them.

The total stopping distance for vehicles equipped with air brakes is made up of four factors: perception distance, reaction distance, brake lag distance, and braking distance. When braking at a speed of 55 mph while driving on dry pavement, the brake lag can add around 32 feet to a vehicle's total stopping distance.

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.

In work zones, you should observe posted speed limits. Slow down if road or weather conditions are poor, and slow down even further if workers are near the roadway.

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.