Nevada CDL: Combination Vehicles Practice Test

Not quite. The answer is Bobtail tractors can take longer to stop than fully loaded combination vehicles.

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 your brakes might fail.

On a combination vehicle, the brakes on the tractor and all trailers must work properly. If your combination vehicle is equipped with air brakes, check that air flows to all trailers and test both the trailer service brakes and the trailer emergency brakes.

Not quite. The answer is Neutral

Before you inspect the trailer supports of the landing gear, secure the tractor by applying the parking brake and placing the transmission in Neutral.

Not quite. The answer is fully loaded

The weight of cargo helps the wheels get traction. 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.

Not quite. The answer is there is enough clearance between the tractor frame and the landing gear to accommodate sharp turns.

After you've coupled the trailer and fully raised the landing gear, check that there is enough clearance between the rear of the tractor frame and the landing gear so they won't make contact even on sharp turns.

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 Upper and lower fifth wheel, air lines, and electrical lines

When making a visual check of the coupling, be sure to check the upper and lower fifth wheel, air lines, and electrical lines.

Not quite. The answer is applying and releasing the trailer brakes and listening for brake sounds.

After you've connected the air lines, double-check the connection and make sure the brakes are working. Shut off the engine so you can hear the brakes. Apply the brakes and listen for the sound of the brakes being applied. Release the brakes and listen for the hiss of escaping air.

Not quite. The answer is two red lights

According to federal regulations, if the load projects more than 4 feet behind the rear of the vehicle, the end of the load must be marked as follows: (1) with two red flags, each 18 inches square, in the daytime; or (2) with two red lights at night. There are additional federal requirements on how to illuminate the rest of the load. US states may impose their own additional requirements on the transportation of oversized loads. You can learn about Nevada's requirements by contacting the Nevada Department of Transportation or visiting their webpage "General Permit Information" (https://www.nevadadot.com/doing-business/commercial-vehicles/commercial-vehicle-permits/general-permit-information). [49 CFR 393.11],

Source: 49 CFR 393.87

Not quite. The answer is the emergency and service air lines.

Before backing under the trailer, you must lock the trailer brakes – which means that you first have to make sure that the trailer brakes are working. Connect the emergency and service air lines and test the trailer brakes.

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 It should not be done.

The trailer hand valve (also known as a spike, a trolley valve, or a Johnson bar) controls only the trailer brakes, not the tractor brakes. If you apply it while you're driving, you'll brake the trailers but not the tractor. This can cause a trailer skid.

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

The trailer air supply valve (which is manually controlled by the red dashboard knob) senses air pressure in the supply (emergency) line. If air pressure in the supply line is lost, the trailer air supply valve will close automatically, and the resulting loss of air pressure in the tractor protection valve will cause it to close as well. And loss of pressure in the supply line will cause the trailer emergency (spring) brakes to come on.

Not quite. The answer is emergency line

The trailer air supply valve (which is manually controlled by the red dashboard knob) senses air pressure in the supply (emergency) line. If air pressure in the supply line is lost, the trailer air supply valve will close automatically, and the resulting loss of air pressure in the tractor protection valve will cause it to close as well. And loss of pressure in the supply line will cause the trailer emergency (spring) brakes to come on.

Not quite. The answer is the brakes on the trailer wheels caused the skid in the first place.

The trailer hand valve (also known as a trolley valve or Johnson bar) controls only the trailer brakes, not the tractor brakes. If you're already jackknifing because the trailer wheels locked up, applying the trailer brakes with the hand valve can make it even worse. Instead, stop braking. The rear wheels will start to roll again and you can steer to correct the skid.

Not quite. The answer is The rear wheels of the last trailer

Off-tracking is defined as the different paths taken by the front and rear wheels in a turn. The longer the vehicle, the greater the difference will be. Thus, the wheels on the front trailer will offtrack more than the tractor's rear wheels, and the wheels on the rearmost trailer will offtrack most of all.

Not quite. The answer is With the tractor frame under the trailer

After you've unlocked the fifth wheel, pull the tractor forward until the fifth wheel is out from under the trailer but the tractor frame is still under the trailer. This will prevent the trailer from falling onto the ground should the landing gear fail to support the trailer.

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 empty.

Trucks brake best when they are used as they were designed: to carry a properly balanced load. 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.

Not quite. The answer is It is used to supply the trailer with air, shut the air off, and apply the trailer emergency brakes.

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. Pulling out the knob shuts off the flow of air and causes the trailer emergency brakes to come on.