CDL Combination Vehicle License Exam Sample Test
A combination vehicle is one that connects a tractor to one or more trailers. These vehicles are used to transport heavy objects and, due to their uniqueness, need a different driving license other than the normal commercial one. If you are training to get your CDL, the combination vehicle test below is for you. Give it a shot and drive safe.
Questions and Answers
- 1.
You are driving a combination vehicle. If the service air line comes apart but the emergency line stays together, what will happen right away?
- A.
The trailer's air tank with exhaust through the open line.
- B.
The emergency trailer brakes will come on.
- C.
Nothing is likely to happen until you try to apply the brakes.
Correct Answer
C. Nothing is likely to happen until you try to apply the brakes.Explanation
If the service air line comes apart but the emergency line stays together, nothing is likely to happen until you try to apply the brakes. This is because the service air line is responsible for supplying air to the trailer's brakes, while the emergency line is used in emergency situations to activate the trailer's brakes. Since the emergency line is still intact, the trailer's brakes will not be affected until the brakes are actually applied.Rate this question:
-
- 2.
If you cannot make a turn without entering another traffic lane, you should:
- A.
Turn wide before you start your turn.
- B.
Turn wide as you complete your turn.
- C.
Not make that turn.
Correct Answer
B. Turn wide as you complete your turn.Explanation
When you cannot make a turn without entering another traffic lane, it is important to turn wide as you complete your turn. This means that you should start your turn from the appropriate lane, but as you complete the turn, you should swing out slightly into the adjacent lane to ensure that you have enough space to navigate the turn safely. This allows you to avoid cutting the corner too sharply and potentially colliding with other vehicles or objects.Rate this question:
-
- 3.
When should you use chocks to park a trailer not equipped with spring brakes?
- A.
Never
- B.
Always
- C.
Only when it will be parked on an incline.
Correct Answer
B. AlwaysExplanation
Chocks should always be used to park a trailer not equipped with spring brakes. Chocks are wedge-shaped blocks that are placed behind the wheels of a vehicle to prevent it from rolling. When a trailer does not have spring brakes, which are designed to automatically engage when the air pressure is lost, chocks become essential for ensuring that the trailer remains stationary and does not accidentally roll away. Therefore, it is necessary to use chocks whenever parking a trailer without spring brakes to ensure safety and prevent any potential accidents.Rate this question:
-
- 4.
In general, the higher your truck's "center of gravity", the:
- A.
Easier it is to turn around corners.
- B.
More stable it is when turning.
- C.
Easier it is to turn over.
Correct Answer
C. Easier it is to turn over.Explanation
The higher the truck's center of gravity, the easier it is to turn over. This is because a higher center of gravity makes the truck more top-heavy and prone to tipping over during turns.Rate this question:
-
- 5.
One of the things a driver can do to prevent a rollover is to keep:
- A.
Both hands firmly on the steering wheel.
- B.
The cargo as close to the ground as possible.
- C.
The fifth wheel free play as small as possible.
Correct Answer
B. The cargo as close to the ground as possible.Explanation
Keeping the cargo as close to the ground as possible can help prevent a rollover because a lower center of gravity reduces the likelihood of the vehicle tipping over. When the cargo is positioned higher, it raises the vehicle's center of gravity, making it more unstable and prone to rolling over. By keeping the cargo low, the driver can maintain better control over the vehicle and reduce the risk of a rollover accident.Rate this question:
-
- 6.
The trailer air supply control (or tractor protection valve control) should automatically close when the air pressure falls between ______ psi.
- A.
20 and 45
- B.
60 and 85
- C.
100 and 125
Correct Answer
A. 20 and 45Explanation
The trailer air supply control (or tractor protection valve control) should automatically close when the air pressure falls between 20 and 45 psi. This is because the trailer air supply control is designed to protect the trailer's air supply system. If the air pressure falls below 20 psi, it indicates a potential leak or problem in the system. Similarly, if the air pressure exceeds 45 psi, it could cause damage to the trailer's air system. Therefore, the control is programmed to close within this range to ensure the safety and proper functioning of the trailer's air supply.Rate this question:
-
- 7.
A trailer is most likely to jackknife when it is:
- A.
Loaded to full capacity.
- B.
Over loaded.
- C.
Empty.
Correct Answer
C. Empty.Explanation
When a trailer is empty, it has less weight and less traction on the road. This lack of weight on the trailer's wheels can cause them to lock up and skid, leading to a jackknife situation. In contrast, when the trailer is loaded to full capacity or overloaded, it has more weight and better traction, reducing the likelihood of jackknifing. Therefore, an empty trailer is most likely to jackknife.Rate this question:
-
- 8.
You are driving a combination vehicle. The trailer breaks away and pulls apart both air lines. You would expect the trailer brakes to come on and the:
- A.
Tractor to lose all air pressure.
- B.
Trailer supply valve to stay open.
- C.
Tractor protection valve to close.
Correct Answer
C. Tractor protection valve to close.Explanation
When the trailer breaks away and pulls apart both air lines, it causes a loss of air pressure in the tractor. The tractor protection valve is designed to close automatically when there is a significant loss of air pressure, which is the case in this scenario. This valve prevents the loss of air pressure from affecting the tractor's brake system, ensuring that the tractor can still maintain its braking ability even when the trailer breaks away. Therefore, the tractor protection valve closing is the expected outcome in this situation.Rate this question:
-
- 9.
The front trailer supports are up and the trailer is resting on the tractor. Make sure:
- A.
There is enough clearance between the upper and lower fifth wheel.
- B.
The safety latch is in the unlocked position.
- C.
There is enough clearance between the tractor frame and landing gear.
Correct Answer
C. There is enough clearance between the tractor frame and landing gear.Explanation
The correct answer is that there is enough clearance between the tractor frame and landing gear. This is important because if there is not enough clearance, it could cause damage to the tractor frame or landing gear when the trailer is resting on the tractor. It is important to ensure that there is sufficient space between these two components to prevent any potential issues or accidents.Rate this question:
-
- 10.
You are coupling a tractor to a semitrailer. You have backed up but are not under it. What should you hook up before backing under a semitrailer?
- A.
The emergency and service air lines.
- B.
The electrical service cable.
- C.
Nothing. Back up and lock the fifth wheel.
Correct Answer
A. The emergency and service air lines.Explanation
Before backing under a semitrailer, it is necessary to hook up the emergency and service air lines. This is important because these air lines provide the necessary braking and control functions for the semitrailer. By connecting these lines, the tractor can communicate with the trailer's braking system, allowing the driver to control the trailer's movements while backing up. This ensures safe and effective maneuvering of the vehicle combination.Rate this question:
-
- 11.
Which part of the kingpin should the locking jaws close around?
- A.
The shank.
- B.
The head.
- C.
The base.
Correct Answer
A. The shank.Explanation
The correct answer is the shank. The shank refers to the part of the kingpin that connects to the trailer. It is a cylindrical or tapered piece that fits into the coupling mechanism of the fifth wheel. Closing the locking jaws around the shank ensures a secure connection between the tractor and the trailer, preventing any potential separation during transportation. The head and base are not the appropriate parts for the locking jaws to close around in this context.Rate this question:
-
- 12.
You should not back a tractor under a trailer until the whole air system is:
- A.
Empty.
- B.
At normal pressure.
- C.
Between 60 and 80 psi.
Correct Answer
B. At normal pressure.Explanation
Before backing a tractor under a trailer, it is important to ensure that the whole air system is at normal pressure. This is because the air system is responsible for controlling the brakes on both the tractor and the trailer. If the air system is not at normal pressure, it could affect the braking performance, making it unsafe to back the tractor under the trailer. Therefore, it is crucial to wait until the air system is at normal pressure before attempting to back the tractor under the trailer.Rate this question:
-
- 13.
You want to inspect the trailer supports. You should place the tractor transmission in which gear after you have uncoupled the trailer?
- A.
Low reverse.
- B.
Neutral.
- C.
High reverse.
Correct Answer
B. Neutral.Explanation
After uncoupling the trailer, placing the tractor transmission in neutral would be the most appropriate gear. This is because neutral disengages the transmission from the engine, allowing the tractor to remain stationary without applying any power or torque. It provides a safe and stable position for inspecting the trailer supports without any risk of the tractor moving unintentionally. Low reverse and high reverse gears are not suitable in this scenario as they would engage the transmission and potentially cause the tractor to move backwards, posing a safety hazard.Rate this question:
-
- 14.
What will happen if the air lines are crossed when you hook up to an old trailer with no spring brakes?
- A.
The hand valve applies the tractor brakes instead of the trailer brakes.
- B.
You could drive away with no trailer brakes.
- C.
The brake lights will not come on when you press the brake pedal.
Correct Answer
B. You could drive away with no trailer brakes.Explanation
If the air lines are crossed when hooking up to an old trailer with no spring brakes, it means that the hand valve will apply the tractor brakes instead of the trailer brakes. This would result in the trailer having no brakes at all. Therefore, if the driver were to drive away in this situation, they would be driving with no trailer brakes, which could be dangerous and potentially lead to accidents or difficulty in controlling the vehicle.Rate this question:
-
- 15.
After you supply air to the trailer, make sure the air lines are not crossed and the trailer brakes are working. You do this by:
- A.
Turning on the parking brakes from the cab.
- B.
Watching your mirrors to see if the trailer lights come on.
- C.
Applying/releasing the trailer brakes and listening for brake sounds.
Correct Answer
C. Applying/releasing the trailer brakes and listening for brake sounds.Explanation
The correct answer is applying/releasing the trailer brakes and listening for brake sounds. This is the correct way to ensure that the trailer brakes are working properly after supplying air to the trailer. By applying and releasing the trailer brakes, you can test if they engage and disengage properly. Additionally, listening for brake sounds can help identify any issues with the brakes, such as squeaking or grinding noises, which may indicate a problem that needs to be addressed.Rate this question:
-
- 16.
Which of these statements is true?
- A.
The brake suspension system of combination vehicles work best with a light load.
- B.
Light vehicles need more braking power to stop than heavy ones.
- C.
"Bobtail" tractors can take longer to stop than a combination vehicle.
Correct Answer
C. "Bobtail" tractors can take longer to stop than a combination vehicle.Explanation
"Bobtail" tractors can take longer to stop than a combination vehicle because combination vehicles have the added weight and braking power of the trailer. The additional weight and braking power of the trailer helps to stabilize the vehicle and provide more traction, allowing for shorter stopping distances. On the other hand, "bobtail" tractors, which are tractors without a trailer, have less weight and braking power, making it more difficult to stop quickly.Rate this question:
-
- 17.
Loss of air pressure in the emergency line causes:
- A.
The relay valves to close.
- B.
An increase in air pressure to the service line.
- C.
The trailer's emergency brakes to come on.
Correct Answer
C. The trailer's emergency brakes to come on.Explanation
When there is a loss of air pressure in the emergency line, it causes the trailer's emergency brakes to come on. This is because the emergency brakes are designed to activate when there is a loss of air pressure in the system, ensuring that the trailer comes to a stop in case of an emergency or if it becomes detached from the towing vehicle. The relay valves closing and an increase in air pressure to the service line are not directly related to the loss of air pressure in the emergency line.Rate this question:
-
- 18.
Why should you be sure that the fifth wheel plate is greased as required?
- A.
To ensure good electrical connections.
- B.
To prevent steering problems.
- C.
To reduce heat and noise.
Correct Answer
B. To prevent steering problems.Explanation
Greasing the fifth wheel plate as required is important to prevent steering problems. The fifth wheel plate is the connection point between the tractor and trailer, and it allows for smooth and controlled movement during turns. If the fifth wheel plate is not properly greased, it can lead to excessive friction and wear, causing difficulties in steering. Adequate lubrication ensures that the fifth wheel operates smoothly, reducing the risk of steering issues and promoting safe and efficient maneuverability.Rate this question:
-
- 19.
Glad hands are used to connect the:
- A.
Electric lines from the truck to the trailer.
- B.
Kingpin from the tractor to the locking jaws on the glide side.
- C.
Service and emergency air lines from the truck to the trailer.
Correct Answer
C. Service and emergency air lines from the truck to the trailer.Explanation
Glad hands are used to connect the service and emergency air lines from the truck to the trailer. This allows for the transfer of air between the two vehicles, which is crucial for the operation of the trailer's brakes. The glad hands create a secure and airtight connection, ensuring that the air pressure is properly maintained and that the brakes can be applied and released as needed.Rate this question:
-
- 20.
When should you use the hand valve to park a combination vehicle?
- A.
To park at loading docks.
- B.
To park on a grade.
- C.
Never.
Correct Answer
C. Never.Explanation
The hand valve should never be used to park a combination vehicle. The hand valve is used to apply the emergency brakes on the trailer, and it should only be used in emergency situations. Parking a combination vehicle should be done by applying the parking brake, not the hand valve.Rate this question:
-
- 21.
A tractor with a(n) ________ trailer requires the shortest stopping distance.
- A.
Empty.
- B.
Lightly loaded.
- C.
Fully loaded.
Correct Answer
C. Fully loaded.Explanation
A tractor with a fully loaded trailer requires the shortest stopping distance because the additional weight increases the traction between the tires and the road, allowing for better braking performance. The increased weight also adds more stability to the vehicle, reducing the risk of skidding or losing control during braking. Conversely, an empty or lightly loaded trailer would have less traction and stability, requiring a longer stopping distance.Rate this question:
-
- 22.
Under good driving conditions, you should leave at least one second of space between your vehicle and the vehicle ahead for every ______ feet of your vehicle's length.
- A.
10
- B.
20
- C.
30
- D.
Option 4
Correct Answer
A. 10Explanation
Under good driving conditions, it is recommended to leave at least one second of space between your vehicle and the vehicle ahead for every 10 feet of your vehicle's length. This is important to ensure a safe following distance and allow for adequate reaction time in case of any sudden changes or emergencies on the road.Rate this question:
-
- 23.
When you are uncoupling a loaded trailer, lower the landing gear until it:
- A.
Makes firm contact with the ground.
- B.
Makes contact with the ground and lifts the trailer off of the fifth wheel.
- C.
Just reaches the ground.
Correct Answer
A. Makes firm contact with the ground.Explanation
When uncoupling a loaded trailer, it is important to lower the landing gear until it makes firm contact with the ground. This ensures that the trailer is stable and secure while it is being detached from the fifth wheel. If the landing gear only just reaches the ground or lifts the trailer off of the fifth wheel, it may not provide enough support and could potentially cause the trailer to tip or become unbalanced. Therefore, making firm contact with the ground is the correct procedure to follow when uncoupling a loaded trailer.Rate this question:
-
- 24.
You have uncoupled a trailer and you want to inspect the landing gear. The tractor should be positioned:
- A.
With the tractor frame under the trailer.
- B.
Completely clear of the trailer.
- C.
With the fifth wheel directly beneath the kingpin.
Correct Answer
A. With the tractor frame under the trailer.Explanation
When inspecting the landing gear of a trailer after uncoupling it, it is important to position the tractor with its frame under the trailer. This ensures stability and prevents any potential accidents or damage. By having the tractor frame under the trailer, it provides support and balance while inspecting the landing gear. It also allows for easy re-coupling when the inspection is complete.Rate this question:
-
- 25.
When checking the trailer's emergency brakes, the tractor protection control valve should be placed in the _____ position.
- A.
Normal
- B.
Neutral
- C.
Emergency
Correct Answer
C. EmergencyExplanation
When checking the trailer's emergency brakes, the tractor protection control valve should be placed in the "Emergency" position. This is because the emergency position allows for the maximum amount of air pressure to be applied to the trailer's brakes, ensuring that they are functioning properly. Placing the valve in the normal or neutral position would not provide the necessary pressure for an accurate assessment of the emergency brakes.Rate this question:
-
Quiz Review Timeline +
Our quizzes are rigorously reviewed, monitored and continuously updated by our expert board to maintain accuracy, relevance, and timeliness.
-
Current Version
-
Mar 22, 2023Quiz Edited by
ProProfs Editorial Team -
Jan 16, 2015Quiz Created by
Devin Hutchings
Back to top