Wisconsin CDL Combination Vehicles Practice Test

A loss of air pressure in the emergency line will cause:

• The suspension springs to extend.
• The tractor protection valve to open.
• The emergency brakes to activate.

The emergency air line controls the emergency brakes on a combination vehicle. A loss of air pressure in the emergency line will cause the emergency trailer brakes to activate.

When connecting a converter dolly to a second trailer, the trailer height should be ____ the center of the fifth wheel.

• Level with
• Slightly higher than
• Slightly lower than

When connecting a converter dolly to a second or third trailer, the trailer height should correct. It should be slightly lower than the center of the fifth wheel.

In a sudden turn, the ____ trailer is the most likely to turn over.

• Front
• Last
• Middle

When making a turn, be sure to steer gently and smoothly. Making a quick turn while pulling trailers is dangerous and can increase the risk of the last trailer rolling over.

After completing a pre-trip inspection, you should ensure that the:

• Service line valve is closed.
• Trailer hand brake is applied.
• Emergency line valve is open.

Before a trip, you should ensure that air reaches all air brakes on all trailers by opening up the rear emergency line and service line shut-off valves and listening for escaping air. Close both shut-off valves before beginning to drive.

All trailers made after ____ must be equipped with Anti-Lock Braking Systems (ABS).

• 1943
• 1998
• 2009

All trailers and converter dollies manufactured on or after March 1, 1998 must have Anti-Lock Braking Systems (ABS).

An air supply control lever should be in its "normal" position when you are:

• Changing a tire.
• Applying the trailer emergency brakes.
• Pulling a trailer.

Tractor protection controls in older vehicles may be operated by levers instead of knobs. If an air supply control is set in its "normal" position, it is properly set for you to pull a trailer.

How much space should be between the upper and lower fifth wheel?

• About five inches of space
• A maximum of two inches of space
• No space

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

In a vehicle equipped with an automatic tractor protection valve, the valve will pop out when:

• Air pressure drops to a level between 20 and 45 psi.
• You are experiencing a trailer jackknife.
• Wheels have regained traction after a skid.

In vehicles equipped with an automatic tractor protection valve, the valve will pop out if air pressure drops to a level between 20 and 45 psi. When the valve pops out, the protection valve will close, stopping the flow of air.

Which of the following will not help prevent a rig from rolling over?

• Keeping the cargo as close to the ground as possible
• Driving slowly around turns
• Driving on the shoulder of a road

To help prevent a rig from rolling over, you should keep the weight of the cargo as close to the ground as possible when loading. You should also drive slowly around turns.

Push in the trailer air supply control to:

• Activate the emergency brakes.
• Deactivate the air brakes.
• Supply the trailer with air.

Push in the trailer air supply control to supply the trailer with air. Pull out the trailer air supply control to turn off the air supply and activate the emergency brakes.

To test the trailer service brakes, you should:

• Move the vehicle forward slowly and apply the brakes with the brake pedal.
• Reverse the vehicle slowly and apply the brakes with the hand control.
• Move the vehicle forward slowly and apply the brakes with the hand control.

To test the trailer service brakes, you should first ensure that the braking system has a normal air pressure level, then release the parking brake. You should then move the vehicle forward slowly and apply the brakes with the hand control. If the trailer service brakes are working properly, you will feel the brakes activate.

During a trip, the ____ should be open.

• Rear service line shut-off valve
• Rear supply line shut-off valve
• Inner shut-off valves

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 it is not able to escape from the back of the vehicle.

Operating combination vehicles usually requires ­­­­­____ operating single vehicles.

• Less skill than
• About the same level of skill as
• More skill than

Combination vehicles are usually heavier and longer than single combination vehicles. Operating a combination vehicle requires a higher level of driving skill than operating a single commercial vehicle.

To find out if a vehicle that was built before 1998 has an Anti-Lock Braking System (ABS), you can:

• Pump the air brakes to activate the ABS.
• Look into the back of the fifth wheel.
• Check for wheel speed sensors coming from the back of the brakes.

If you are operating a vehicle built before 1998 and are unsure if the trailer has an Anti-Lock Braking System (ABS), you can check under the trailer for wheel speed sensors coming from the back of the brakes.

What does an Anti-Lock Braking System (ABS) do?

• It allows a vehicle's wheels to lock up.
• It prevents a vehicle's wheels from locking up.
• It makes turning a vehicle easier.

An Anti-Lock Braking System (ABS) helps prevent wheel lockup during hard braking. If ABS detects impending lockup, it reduces braking pressure to a safe level.

The emergency air line supplies air to the:

• Relay valves.
• Trailer air tanks.
• Signal line.

The emergency air line (also known as the supply line) has two functions. The first is to supply air to the trailer air tanks, and the second is to control the emergency brakes on combination vehicles.

The ____ trailer is the most likely to turn over if a driver takes a turn too quickly.

• Front
• Last
• Middle

When making a turn, be sure to steer gently and smoothly. Making a quick turn while pulling trailers is dangerous and can increase the risk of the last trailer rolling over.

If you must cross traffic while driving a combination vehicle, you should:

• Assume other drivers will make room for your vehicle.
• Wait for a gap large enough for your vehicle to safely cross.
• Rely only on your mirrors.

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 enonugh gap in traffic to safely do so.

The trailer hand valve should not be used while you are driving because:

• It will disconnect from the vehicle.
• You will stop the vehicle too quickly.
• It can cause a skid.

Never use the trailer hand valve while operating your vehicle. Using the trailer hand valve while driving can cause your trailer to skid.

Keeping cargo centered on a rig can:

• Help you drive faster.
• Prevent a rollover.
• Make turns more dangerous.

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.

Trailers with low underneath clearance may be difficult to drive:

• On interstate highways.
• Over railroad crossings.
• On dirt roads.
• At the posted speed limit.

Railroad-highway crossings may be difficult to cross when pulling a trailer with a low underneath clearance. In particular, both low-slung units and single-axle tractors pulling long trailers are especially challenging to drive over raised crossings.

After connecting the air lines to the trailer while coupling, you should:

• Supply air to the trailer.
• Chock the wheels.
• Inspect the fifth wheel.

Correctly following the steps to couple and uncouple trailers is vital to safely operating a combination vehicle. After connecting the air lines to the trailer while coupling, you should supply air to the trailer.

When entering or crossing traffic while driving a combination vehicle, it is especially important that you:

• Sound your horn.
• Make sure there is a large enough gap for your vehicle.
• Expect other drivers to make room for your vehicle.

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.

Trailers built before 1975 are:

• Required to have spring brakes.
• Not required to have spring brakes.
• Unsafe to drive.

Trailers built before 1975 are not required to have spring brakes. When parking a trailer without spring brakes, be sure to use wheel chocks to prevent the trailer from rolling.

Test the tractor protection valve by:

• Removing the air supply knob.
• Removing the parking brake control knob.
• Releasing air with the brake pedal.
• Releasing air with the gas pedal.

You should test the tractor protection valve by allowing the air supply to properly charge, turning off the engine, then releasing air from the system by pressing the brake pedal several times. The tractor protection valve should move into its emergency position when psi drops to an unsafe level.