Arizona CDL: Combination Vehicles Practice Test

Not quite. The answer is make sure the ground is solid and can support the weight of the trailer.

Before uncoupling the trailer, be sure you're leaving it on firm ground that can support its weight.

Not quite. The answer is carries air to a relay valve that allows the trailer brakes to be applied quickly.

The service line (also called the control line or signal line) carries air, which is controlled by the foot brake or the trailer hand brake. The service line is connected to relay valves that allow the trailer brakes to be applied more quickly. The relay valves send air to the brake chambers in response to the air pressure in the service line.

Not quite. The answer is Gently pull forward in low gear against the locked trailer brakes; then look at it carefully.

After you've backed under the trailer and locked the kingpin into the fifth wheel, raise the landing gear slightly. Then with the trailer brakes still locked, gently pull the tractor forward to check that the trailer is locked onto the tractor.

Not quite. The answer is "Bobtail" tractors can take longer to stop than fully loaded tractor-trailers.

When a combination vehicle is empty or lightly loaded, its braking distance increases. The very stiff suspension springs and strong brakes give poor traction and make it very easy to lock the wheels. Likewise, "bobtail" tractors (tractors without semitrailers) can take longer to stop than a fully loaded tractor-trailer. Be very careful when driving a "bobtail" tractor.

Not quite. The answer is pushing in the trailer air supply control.

On newer vehicles, the trailer air supply control is an eight-sided red knob on the dashboard of the tractor. The knob may be labeled "Pull to exhaust...Push to supply" or something similar. When you push the knob in, air will flow through the trailer's emergency air lines to charge the trailer air brake system.

Not quite. The answer is In the rear

The shut-off valves are located at the rear of a trailer, since that is where they must be located to service the air lines. The shut-off valves are open except in the last trailer, in which they are closed.

Not quite. The answer is go slowly around turns.

Because of rearward amplification, a trailer is more likely to roll over than a tractor. And if you're pulling doubles or triples, the rearmost (last) trailer is even more likely to roll over. To reduce the risk of trailer rollover, steer gently and smoothly, especially if you're pulling a double or triple. Slow down before entering a curve or turn.

Not quite. The answer is (a) The tractor is on level ground.

When coupling a trailer to a tractor, it's a good idea to make sure that you're on a level surface free of dips or potholes. If you back the tractor over a large bump, dip, or pothole, you might damage something as you attempt to push the tractor underneath the trailer. On the other hand, the trailer itself need not be perfectly level. You want it to be aligned so that it will be raised slightly when the tractor is backed underneath it.

Not quite. The answer is To engage the trailer brakes in case of air pressure loss

The emergency air line has two main functions: (1) It supplies air to the trailer air tanks to keep the trailer brake system charged. (2) It controls the vehicle's emergency brakes. If air pressure in the emergency air line drops too low (say because of a bad leak or damage due to the trailer breaking loose), the trailer emergency brakes will come on. Also, the tractor protection valve will close to keep air from escaping from the tractor.

Not quite. The answer is Normal

To test the trailer air brake system, first charge it with air. Push in the red trailer air supply knob, or place the tractor protection valve control in the "normal" position. Wait until the air pressure reaches normal before you start your tests.

Not quite. The answer is slightly raised.

After you've backed under the trailer and locked the kingpin into the fifth wheel, raise the landing gear slightly. Then with the trailer brakes still locked, gently pull the tractor forward to check that the trailer is locked onto the tractor.

Not quite. The answer is at normal pressure.

During the coupling process, after you have connected the tractor air lines to the trailer, push in the trailer air supply valve to fully charge the trailer air brake system with compressed air. Make sure that the trailer air brakes are working before you proceed with the rest of the coupling process.

Not quite. The answer is It will keep dirt and water out of the lines.

Some vehicles are equipped with "dead-end" or dummy couplers. When the air lines are not connected to a trailer, connect the glad hands to the dummy couplers to keep water and dirt out of the glad hands and air lines. If your vehicle doesn't have dummy couplers, you may be able to connect the glad hands to each other.

Not quite. The answer is check the air line connections.

If you cross the emergency and service air lines, air will flow to the service line instead of the trailer air tanks. Air won't be available to release the spring brakes. Therefore, if the spring brakes don't release when you push the trailer air supply control, check the air line connections.

Not quite. The answer is Fully raised with the crank handle secured in its bracket

Once you've coupled, raise the landing gear all the way up. If it's only partially raised, it could catch on something, such as the railroad tracks on a raised railroad crossing.

Not quite. The answer is there is less traction.

Trucks that are empty or only lightly loaded take longer to stop because the stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.

Not quite. The answer is Push in the trailer air supply valve control.

The control for the trailer air supply valve is an eight-sided red knob on the dashboard. You push the knob in to supply compressed air to the trailer air brake system. You pull the knob out to evacuate air from the trailer air brake system (which will set the trailer brakes).

Not quite. The answer is a Class A CDL with a Doubles/Triples (T) endorsement.

To legally pull a trailer whose gross vehicle weight rating (GVWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. To pull triples, you'll also have to obtain a Doubles/Triples (T) endorsement on your CDL. Note: If you don't also pass a knowledge test on air brakes, your CDL will include restriction L, limiting you to driving only vehicles without air brakes.

Not quite. The answer is glad hands

As part of your vehicle inspection test, if your vehicle is equipped with air brakes and has a trailer, you will inspect the air connections between the truck or tractor and the trailer. These connections are made with hose couplers (commonly called "glad hands" because they vaguely resemble shaking hands). These glad hands have rubber seals to form a tight connection and prevent air from escaping. Make sure that the glad hands are locked in place and free of damage or air leaks.

Not quite. The answer is keep the cargo as close to the ground as possible.

The higher the truck's center of gravity, the more likely it is to roll over. If the cargo is to one side, it will make the trailer lean, which can also make a rollover more likely. To help prevent a rollover, spread your cargo evenly and keep it as low as possible.