Utah CDL DMV Combination 1

The easiest way to become aware that your trailer has begun to skid is to observe it in your mirrors. Checking your trailer in your mirrors will also allow you to spot any skidding at the earliest possible moment.

The tractor protection valve keeps air in the trailer's braking system should the trailer break away or develop a leak. A loss of air pressure in the emergency line will cause the tractor protection valve to open and the emergency trailer brakes to activate.

Be sure to test the trailer emergency brakes before beginning a trip. After ensuring that the trailer rolls freely, you can test the emergency brakes by pulling out the trailer air supply control, or placing it in the "emergency" position. Pull forward slightly with the tractor and make sure the trailer does not move.

Tractors without semi-trailers are referred to as bobtail tractors. Operating a bobtail tractor requires drivers to exercise caution.

On combination vehicles with air brakes, the tractor protection valve keeps air in the tractor or truck brake system, should the trailer develop a bad leak or break away from the tractor.

Knowing proper coupling and uncoupling technique is fundamental to the safe operation of combination vehicles. Improper coupling can be very dangerous.

An empty combination vehicle will come to a complete stop more slowly than a fully-loaded vehicle. With less weight in a trailer, the stiff suspension springs and strong brakes will have lower traction than they would if the vehicle carried more weight.

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.

An empty trailer will require a longer stopping distance than a loaded trailer. Additionally, a trailer is most likely to swing out and strike other vehicles when it is lightly loaded or empty.

The trailer hand valve (also referred to as the "trolley valve" or "Johnson bar") works the trailer brakes and should be used only when testing them. Using the trailer hand valve while driving could result in a skid.

When coupling air brake hoses, you should make sure the proper pairs of gland hands are connected. They are sometimes color-coded to help drivers avoid mistakes. Typically, blue is used for service lines and red is used for emergency lines.

Combination vehicles have two air lines: a service line and an emergency line.

Correctly following the steps to couple and uncouple trailers is vital to safely operating a combination vehicle. Before backing your tractor under the trailer while coupling, make sure your trailer brakes are locked.

To reduce the risk of tipping over when driving with a trailer, you should steer gently and smoothly. Avoid making sudden movements.

Be sure to test the trailer emergency brakes before beginning a trip. After ensuring that the trailer rolls freely, you can test the emergency brakes by pulling out the trailer air supply control, or placing it in the "emergency" position. Pull forward slightly with the tractor and make sure the trailer does not move.

If your vehicle gets stuck on railroad tracks for any reason, you should immediately exit the vehicle and walk away from the tracks. Contact the proper emergency authorities.

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.

When a vehicle goes around a corner, the rear wheels follow a different path than the front wheels. This is called off-tracking. This effect is especially pronounced on vehicles with trailers.

While inspecting a coupling, you should go under the trailer and look into the back of the fifth wheel. Ensure that the fifth wheel jaws are secured around the shank of the kingpin.

Incorrect coupling and uncoupling of combination vehicles can have extremely dangerous consequences.

When starting a trip, be sure that all shut-off valves are in the open position, except for the last valves on the rear trailer. It is important that air reaches the brakes on all trailers and that the air is not able to escape from the back of the vehicle.

A rollover is more likely if cargo is unevenly loaded in a rig. To help prevent a dangerous rollover, it is important to keep a load as centered on the rig as possible.

On newer vehicles, the trailer air supply control is an eight-sided red knob. It's used to control the tractor protection valve.

If you do not know whether or not a trailer is equipped with ABS, look under the vehicle for the electronic control unit and wheel speed sensor wires coming from the back of the brakes.

When backing a vehicle with a trailer, you must turn the steering wheel in the direction opposite of where you want to go. Once your trailer starts to turn, you should turn the steering wheel the other way to follow the trailer.

Driving a combination vehicle usually requires more skill than driving a single vehicle. Combination vehicles are generally longer and heavier than single commercial vehicles.

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

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.

If a vehicle has anti-lock brakes on just one axle, the driver will still have more control during braking than they would without any anti-lock brakes.

Combination vehicles require more space on the road than other vehicles. When entering or crossing traffic while driving a combination vehicle, it is especially important that there is a large enough gap in traffic for you to safely do so.