Colorado CDL: Combination Vehicles Practice Test

Not quite. The answer is directly in front of the trailer.

When you're ready to couple, position your tractor right in front of the trailer. If you were to back into the trailer at an angle, you might push it sideways and break the landing gear.

Not quite. The answer is the coupling is not right and should be fixed before you drive the coupled unit.

Don't drive the vehicle until you're sure that the coupling is correct. Check to make sure of the following: There is no space between the upper and lower fifth wheel, the fifth wheel jaws have closed around the shank of the kingpin, the locking lever is in the "lock" position, and the safety latch is in position over the locking lever. If anything isn't right, don't drive the vehicle until you've found and corrected the problem. If you drive it anyway, your trailer could come loose while you're driving.

Not quite. The answer is It controls the emergency brakes on combination vehicles.

The emergency air line is often colored red. It supplies air to the trailer air tanks and controls the emergency brakes on combination vehicles.

Not quite. The answer is the coupling surface of the trailer is just below the middle of the tractor fifth wheel.

The tractor fifth wheel should tilt downward toward the trailer. As you start to back the tractor under the trailer, the coupling surface of the trailer should be just below the middle of the tractor fifth wheel.

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 Rear

The shut-off valve should be closed only at the rear of the last trailer so that air will flow to the brakes of all trailers but no farther.

Not quite. The answer is Pull the tractor ahead gently with the trailer brakes locked.

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 supply air to the trailer system and then pull out the air supply knob.

Before backing under the trailer, check that the trailer brakes are working and then lock the trailer brakes. Once you've attached the air lines, there are a number of checks you should make: Check the glad hand seals. Make sure that the air lines won't be caught or crushed when you back under the trailer. Charge the trailer air brake system and verify that it's working without significant air loss. Then set the trailer air supply control to shut off the air and put on the trailer emergency brakes.

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 open

When uncoupling, unlock the fifth wheel by raising the release handle lock and pulling the release handle to the open position. When you do this, keep your legs and feet well clear of the tractor's rear wheels in case the vehicle moves.

Not quite. The answer is a yellow malfunction lamp on the left side.

A trailer with ABS has a yellow malfunction lamp on either the left front corner or the left rear corner. Make sure you know where to look for it.

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 Turn wide as you complete your turn.

To turn right, you may need to turn wide to help prevent the rear end of your vehicle from overrunning the curb. However, if you swing wide to the left before you turn right, another driver may try to pass you on your right, which can lead to a collision. Instead, start the right turn with the rear of your vehicle as close to the curb as possible and then turn wide as you complete the turn. This will deny drivers room on the right to try to pass you.

Not quite. The answer is B.

If you swing wide to the left before you turn right, another vehicle may try to pass you on your right while you are turning. Instead, as shown in path B, make the right turn with the rear of your vehicle as close to the curb as possible and turn wide as you complete the turn. This will deny other vehicles enough room on the right to try to pass you.

Not quite. The answer is A triple 27-foot trailer

Because of rearward amplification (causing the crack-the-whip effect), the last trailer in a combination vehicle has the highest probability of rolling over. The last trailer in a triple combination is more likely to roll over than the last trailer in a double combination.

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 use controlled or stab braking.

Hard braking and turning at the same time is likely to cause a skid. You should brake in a way that will keep your vehicle in a straight line and allow you to turn if necessary. If you need to brake suddenly to avoid a crash, use controlled braking or stab braking (but don't use stab braking if your vehicle has antilock brakes).

Not quite. The answer is the brakes will fail if the air supply leaks away.

If the trailer lacks spring brakes, make sure you chock the wheels whenever you park. If air pressure leaks away, the trailer's brakes will fail. Without chocks, the trailer could roll away.

Not quite. The answer is It takes 14 seconds to clear a single track and more than 15 seconds to clear a double track.

You can expect it to take more than 15 seconds for a typical tractor-trailer to clear a double track and at least 14 seconds to clear a single track.

Not quite. The answer is a fully loaded trailer

Trucks brake best when they are used as they were designed: to carry a properly balanced load. Empty trucks actually have longer stopping distances than loaded trucks because they have less traction. The stiff suspension springs and strong brakes give poor traction and make it easier to lock the wheels.