New Hampshire CDL: Combination Vehicles Practice Test

Not quite. The answer is makes firm contact with the ground.

When uncoupling a loaded trailer, lower the landing gear until it makes firm contact with the ground. Then crank the landing gear in low gear for a few more turns – just enough to lift some weight off the tractor, but not so much that you lift the trailer off the fifth wheel. This will make it easier to unlatch the fifth wheel now and couple next time.

Not quite. The answer is tilted down toward the rear of the tractor.

Before coupling, make sure that the fifth wheel is in the proper position. For one thing, it should be tilted down toward the rear of the tractor so that the trailer can easily slide into it.

Not quite. The answer is The shank

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 If the trailer has no spring brakes, you will be able to drive away but you won't have trailer brakes.

Trailers built before 1975 are not required to have spring brakes. If you cross the air lines when coupling such a trailer, you may have no air pressure to supply the trailer brakes. You'll be able to drive, but you won't be able to brake the trailer. Always test the trailer air brakes before you start to drive.

Not quite. The answer is Yes, if you're not sure of your path of travel.

Backing a combination vehicle is potentially hazardous. Before you start to back up, check your intended path of travel. Exit the cab and walk around the vehicle. Check your clearance to the sides and overhead, in and near the path of your vehicle.

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 "Bobtail" tractors can take longer to stop than a combination vehicle loaded to the maximum gross weight.

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 A 5-axle tractor towing a 52-foot trailer

When any vehicle turns, its rear wheels will follow a shorter path than its front wheels. This is called off-tracking or "cheating." The longer the vehicle, the greater the difference. In a combination vehicle, the trailer's wheels will off-track more than the tractor's rear wheels. In a double or triple combination vehicle, the wheels of the last trailer will off-track the most.

Not quite. The answer is whether it is on the tractor or the trailers.

ABS can help prevent wheel locking regardless of whether it's on the tractor, the trailer, or both.

Not quite. The answer is No, because the brakes on the trailer wheels caused the skid to begin with.

The trailer skid was caused by the brakes locking the wheels. Applying the trailer hand brake might make that even worse. Instead, release the brakes so the trailer wheels can roll again and regain traction.

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 at normal pressure.

Before backing under a trailer during the coupling process, make sure that the air pressure is at normal levels so you'll be able to brake safely.

Not quite. The answer is often do not have spring brakes.

Trailers and converter dollies built before 1975 are not required to have spring brakes. Instead, they rely on emergency brakes that hold using air pressure. Because air pressure can leak away, always use wheel chocks when parking such vehicles.

Not quite. The answer is makes firm contact with the ground and takes some weight off the tractor.

When uncoupling a loaded trailer, lower the landing gear until it makes firm contact with the ground. Then crank the landing gear in low gear for a few more turns – just enough to lift some weight off the tractor, but not so much that you lift the trailer off the fifth wheel. This will make it easier to unlatch the fifth wheel now and couple next time.

Not quite. The answer is When you lock the drive wheels on the tractor and the tractor spins out sideways as the trailer continues to push forward

A jackknife is usually the result of a drive-wheel skid. The tractor's rear drive wheels lock, and the trailer starts to push the tractor sideways.

Not quite. The answer is The trailer emergency brakes will come on.

If the emergency (supply) air line breaks, the tractor protection valve will close to stop any more compressed air from leaving the tractor. Hence, the tractor's service brakes should still work. However, the loss of trailer air pressure from the ruptured line will cause the trailer emergency (spring) brakes to come on.

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 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 more

There are more things to inspect on a combination vehicle than on a bus or straight truck. First, of course, there is the entire coupling system: the kingpin, the fifth wheel, etc. Next, there is the landing gear of each trailer. Finally, the air brake system is also more complicated than on a bus or straight truck, because compressed air must flow to all trailers so that both the tractor brakes and trailer brakes will work properly.