Combination Vehicle CDL Practice Test

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Use this free Combination Vehicle commercial drivers license practice test to prepare yourself to get your CLP (commercial learner's permit). To learn more about Roehl's paid CDL training, view our Get Your CDL page or apply now.

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Question 1 of 40

When should you use the hand valve to park a combination vehicle?

To park at loading docks
Never
To park on a grade
Every time

Question 2 of 40

A fully loaded rig is _____ times more likely to roll over in a crash than an empty rig.

5
10
15
20

Question 3 of 40

Which type of truck-trailer combination has the greatest chance of a 'crack-the-whip' rollover?

A tractor pulling two trailers
A single tractor trailer
A tractor pulling three trailers
They all have the same chance of a 'crack-the-whip' rollover

Question 4 of 40

After you lock the kingpin into the fifth wheel, you should check the connection by pulling:

forward 50 feet, then turning right, and then left
the tractor ahead gently with the trailer
the tractor ahead sharply to release the trailer brakes
backward about 10 feet

Question 5 of 40

What is the other name for the shut-off valves?

Relay valves
Tractor protection valve
Emergency valves
Cut-out cocks

Question 6 of 40

What is the first thing you should do to prevent a trailer skid?

Step on the brakes hard several times to stop the skid
Use the trailer hand brake
Recognize that a skid has started to occur in the mirrors
Maintain a constant speed to adjust the truck and trailer in a smooth fashion

Question 7 of 40

You should not use the trailer hand valve while driving because...

you should use the parking brake
it won't work as well as the foot brake
of the danger of making the trailer skid
you could lose the trailer

Question 8 of 40

When following behind other vehicles, you should follow:

at least one second for every 20 feet of your vehicle length
at least two seconds for every 10 feet of your vehicle length
at least two seconds for every 10 feet of your vehicle length, plus one second if going over 50 MPH
at least one second for every 10 feet of your vehicle length, plus one second if going over 40 MPH

Question 9 of 40

A trailer jackknife is likely to happen when:

the vehicle has a high center of gravity
the wheels of the trailer lock up
the front drive wheels lose traction
there is too much weight on the steering axles

Question 10 of 40

What is the emergency air line?

It is an air line that controls the tractor protection valve and emergency valves
It is an air line that is connected to the relay valve to help send air pressure to the trailer air brakes
It is an air line that supplies air to trailer air tanks and controls emergency brakes
It is an air line that connects the trailer air tanks to the trailer air brakes

Question 11 of 40

What is the fastest and best way to recognize that your trailer has started to skid?

Feeling your steering wheel shake
Listening for the distinctive skidding sound
Seeing it in your mirrors
Feeling your vehicle pull to the side

Question 12 of 40

If your trailer begins to skid, you should:

Maintain light pressure on your brakes until the trailer straightens out
Release your brakes until the trailer wheels grip the road again
Turn the steering wheel in the direction of the skid
Apply to the trailer hand brake to straighten out the trailer

Question 13 of 40

Which type of vehicle is harder to control while stopping?

Larger combination vehicles that have no cargo in the trailers
Larger vehicles with no trailers
Larger combination vehicles with loaded trailers
None of these (motorized vehicles all stop at the same rate)

Question 14 of 40

When hoses are not in use, why should the trailer glad hands be locked together or attached to dead end or dummy couplers?

To prevent mix-up the emergency and service lines
To keep the air supply clean
To keep the air supply regulated
To prevent a loss of air pressure

Question 15 of 40

If the tractor protection valve malfunctions, which of the following may occur?

A leak or trailer break away could drain all the air from the brake system
Nothing will happen
The trailer air pressure will increase
The glad hands may uncouple

Question 16 of 40

On older trailers, what will happen if the emergency and service air lines are crossed?

Nothing will happen, they are designed to be interchangeable
The trailer spring brakes will release
Water and oil will build up in the air tanks
You could drive away, but you will not have trailer brakes

Question 17 of 40

What causes the crack-whip effect?

Changing lanes too quickly and suddenly
Driving too fast at turns and curves
None of these (the crack-the-whip effect does not occur in combination vehicles)
Rearward amplification

Question 18 of 40

You should not back a tractor under a trailer until the whole air system is:

at normal pressure
bled down to half the maximum pressure
between 60 and 80 PSI
cleaned

Question 19 of 40

What should you do to prevent the crack-the-whip effect?

Change lanes quickly to avoid the crack-the-whip effect
Drive fast so that you have no chance of causing a crack-the-whip effect
Stay close to the rear of the car in front of you so you can make sure your driving is smooth to avoid hitting the car in front
Steer gently and smoothly when pulling trailers

Question 20 of 40

What is the best way to prevent a rollover?

Place the cargo as close to the ground as possible and drive slowly at turns
Put all cargo in the center of the trailer
Put all cargo anywhere you see fit and drive at normal speeds at turns
Put all cargo on one side of the trailer and drive at posted speeds at turns

Question 21 of 40

What is off tracking?

When truck trailers swing from side-to-side
Swerving on the road when you lose control of your steering
Driving your truck off the road
When the rear wheels go a different path than the front wheels

Question 22 of 40

On the trailer air lines of a combination vehicle, the service line connects to the _____ on the trailer to control the pressure to the trailer brakes.

Glad hands
Trailer hand valve
Relay valves
Tractor protection valve control

Question 23 of 40

What does the tractor protection valve do?

It protects the truck/tractor from skidding
It's another name for trailer emergency brakes which lets air out of the tractor emergency line
It keeps air out of the truck/trailer
It keeps air in the truck/tractor

Question 24 of 40

When does the tractor protection valve close automatically?

It doesn't close automatically, you need to close the valve yourself
When the air pressure is high and reaches 45 to 60 PSI
when the air pressure is low and ranges from 25 PSI to 40 PSI
When the air pressure is low and reaches 30 PSI to 55 PSI

Question 25 of 40

What are the two trailer air lines that every combination vehicle has?

Emergency valve and service line
The service line and emergency line
Air supply line and emergency line
Tractor air supply and tractor protection valve

Question 26 of 40

What is the purpose of the service line?

The service line connects the trailer to the truck/tractor
The service line supplies air to the air tanks
The service line is controlled by the foot brake or trailer hand brake and it carries air
The service line controls foot brakes or trailer hand brake

Question 27 of 40

What are the other names for the service line?

Control line and air supply line
Control line and signal line
Signal line and emergency line
Air pressure line and signal line

Question 28 of 40

What are glad hands?

Coupling devices that connect the service line and emergency line from the truck/tractor to the trailer(s)
Devices that are used to supply air to the trailer air tanks
Devices that are used to fix service and emergency air lines
Devices that are used to connect the service air line to the relay valves

Question 29 of 40

What is the emergency air line?

It is an air line that controls the tractor protection valve and emergency valves
It is an air line that is connected to the relay valves to help send air pressure to the trailer brakes
It is an air line that supplies air to trailer air tanks and controls emergency brakes
It is an air line that connects the trailer air tanks to the trailer air brakes

Question 30 of 40

What does the trailer hand valve do?

It is the valve used to activate the parking brakes
It is used in place of the foot brakes in emergencies
It is the valve that should be activated during driving
It tests the trailer brakes

Question 31 of 40

How many times should you drain the air tanks?

Monthly
Every other day
Once a week
Everyday

Question 32 of 40

What is the first step to coupling tractor semi trailers?

Inspect area and chock wheels
Inspect the fifth wheel
Secure the tractor
Position the tractor in front of the trailer

Question 33 of 40

Which of the following is the best action you could take when the parking brakes don't release?

Change the service and emergency air line connections because they're broken
Check the air line connections
Report it to a supervisor at your earliest convenience
Don't use the spring brakes for any reason

Question 34 of 40

What are trailer air tanks used for?

To supply air pressure to the trailer brakes
To indicate how much air pressure is used on the trailer brakes
To keep oil and water out of the service and emergency air lines
To add more air to tires

Question 35 of 40

What consideration should be made when you park a trailer that doesn't have spring brakes?

Use air pressure from the trailer air tanks
Remove emergency air line
Use wheel chocks
Use the emergency brakes

Question 36 of 40

Which shut-off valves should remain closed?

All shut-off valves should be closed
All shut-off valves should be open
Only the valves on the back of the first trailer should be closed
The valves at the back of the last trailer should remain closed

Question 37 of 40

When doing an inspection, which of the following would best describe a working landing gear?

Secured to the frame
Fully raised and not bent
Greased well
None of these

Question 38 of 40

What is the second step to coupling tractor semi trailers?

Back out slowly until the fifth wheel touches the trailer
Inspect the area and chock the wheels
Check the trailer height
Supply air to the trailer

Question 39 of 40

What happens if the trailer height is too high?

It doesn't matter if the trailer is too high
The tractor may strike and damage the trailer's nose
The spring breaks will not work properly
The trailer may not couple correctly

Question 40 of 40

What is the third step to coupling tractor semi trailers?

Connect air lines to the trailer
Lock the trailer brakes
Secure the tractor
Position the tractor

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