25 realistic Combination Vehicles practice questions for California CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 of 25 · Vehicle Dynamics
Which of these is true about driving combination vehicles?
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A.
They are easier to handle than single vehicles
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B.
They are more likely to roll over and jackknife
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C.
They use less fuel per mile
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D.
They need fewer mirrors
Correct answer: B.
Combination vehicles require more skill and are more prone to rollovers and jackknives.
Question 2 of 25 · Inspection
When should you check trailer brakes during operation?
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A.
First few miles after coupling
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B.
Every fuel stop
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C.
Just at the end of the trip
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D.
Never during the trip
Correct answer: A.
Test trailer brakes early in the trip to make sure they are functioning correctly.
Question 3 of 25 · Coupling
When you finish coupling, the air lines should be:
-
A.
Connected to the proper glad hands and supported off the catwalk and the deck plate
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B.
Coiled tightly on top of the trailer
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C.
Loose so they can move freely
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D.
Disconnected
Correct answer: A.
Air lines must be connected and supported off the deck so they don't snag or wear.
Question 4 of 25 · Vehicle Dynamics
What's the safest way to handle a tight turn with a long combination?
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A.
Take it wide using both lanes if necessary
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B.
Drive as fast as possible to maintain momentum
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C.
Use the trailer hand valve
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D.
Make a tight turn
Correct answer: A.
Take wider turns to avoid hitting curbs or other vehicles due to off-tracking.
Question 5 of 25 · Combination Air
What should the tractor protection valve do?
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A.
Keep tractor air supply if trailer breaks away or develops a major leak
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B.
Set the trailer parking brake on a hill
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C.
Apply trailer brakes during a normal stop
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D.
Disconnect the trailer
Correct answer: A.
It protects the tractor air supply by closing if a major air loss occurs.
Question 6 of 25 · Coupling
When coupling, what should you do after the fifth wheel locks onto the kingpin?
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A.
Pull the tractor forward gently to make sure the kingpin is locked
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B.
Disconnect the air lines
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C.
Drive away immediately
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D.
Release the trailer parking brake first
Correct answer: A.
Tug-test by gently pulling forward with the trailer brakes set to confirm the lock.
Question 7 of 25 · Operation
Which of these is most important when driving with a trailer?
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A.
Use the engine retarder constantly
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B.
Use proper braking and signaling
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C.
Drive at maximum speed limits
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D.
Skip pre-trip checks if running late
Correct answer: B.
Proper braking and clear signaling are essential to safe combination driving.
Question 8 of 25 · Following Distance
What is "rear-end collision" risk for combination vehicles?
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A.
It is reduced when carrying long cargo
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B.
They have a higher risk because of long stopping distances and rear blind spots
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C.
They have no greater risk
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D.
Only for empty rigs
Correct answer: B.
Long stopping distance and rear blind spots increase rear-end collision risk.
Question 9 of 25 · Skids
How can you correct a tractor jackknife?
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A.
Apply the brakes harder
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B.
Steer in the direction of the skid and accelerate gently
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C.
Stop steering input
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D.
Release the brakes and counter-steer
Correct answer: D.
Release the brakes to regain traction; counter-steer carefully to recover.
Question 10 of 25 · Skids
What is "tractor jackknife"?
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A.
Tractor drive wheels skid and the trailer pushes the tractor sideways
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B.
Trailer wheels skid
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C.
Steering wheels skid
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D.
Engine fails
Correct answer: A.
When drive wheels skid, the trailer can push the tractor sideways into a jackknife.
Question 11 of 25 · Coupling
What is the fifth wheel?
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A.
A spare wheel
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B.
A coupling device that connects the tractor to the trailer
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C.
A device on the trailer to support cargo
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D.
A type of axle
Correct answer: B.
The fifth wheel is the round, plate-shaped coupling that connects the tractor to the trailer.
Question 12 of 25 · Skids
Tractor jackknife occurs when:
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A.
Drive wheels lose traction and skid
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B.
The trailer wheels lock
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C.
The trailer slides forward
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D.
Steering wheels lock
Correct answer: A.
Drive wheels skidding cause tractor jackknife; trailer wheels skidding cause trailer jackknife.
Question 13 of 25 · Coupling
What does a "low coupling" condition look like?
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A.
Trailer is too high above the fifth wheel
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B.
Trailer is at the right height
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C.
Trailer is too low and tractor frame can hit the trailer
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D.
Trailer is angled to the right
Correct answer: C.
A trailer too low can damage the tractor frame as it slides under it.
Question 14 of 25 · Coupling
Before backing under a trailer, you should:
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A.
Make sure the trailer brakes are set and the trailer is at the correct height
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B.
Disconnect the air lines
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C.
Lower the landing gear
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D.
Engage the parking brake
Correct answer: A.
Confirm trailer brakes are locked and trailer height matches the fifth wheel.
Question 15 of 25 · Inspection
You should inspect the rear of the trailer for:
-
A.
Cracked or missing lights
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B.
Lights and reflectors are clean and operational
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C.
Mud flap condition
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D.
All of the above
Correct answer: D.
Check lights, reflectors, mud flaps, and license plate during pre-trip.
Question 16 of 25 · Coupling
When uncoupling, you should:
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A.
Lower the landing gear before pulling the kingpin release
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B.
Lift the trailer with the fifth wheel
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C.
Release the parking brake
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D.
Rev the engine
Correct answer: A.
Lower the landing gear so the trailer is supported before disconnecting the kingpin.
Question 17 of 25 · Inspection
Which of these is not a part of the trailer's electrical system?
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A.
Lights
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B.
Brake control
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C.
Power line cord (pigtail)
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D.
Hydraulic pump
Correct answer: D.
Hydraulic pumps are not part of standard trailer electrical systems on highway combinations.
Question 18 of 25 · Cargo
What can cause a high center of gravity?
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A.
Loading cargo too low
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B.
Loading cargo too high or unevenly
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C.
Driving too slowly
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D.
Empty trailers
Correct answer: B.
Stacking cargo too high or loading unevenly raises the center of gravity and rollover risk.
Question 19 of 25 · Combination Air
Trailer brakes are required to be:
-
A.
Adjusted properly and matched to tractor brakes
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B.
Stronger than tractor brakes
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C.
Disengaged on level roads
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D.
Off when empty
Correct answer: A.
Trailer brakes must be in proper adjustment and balance with tractor brakes.
Question 20 of 25 · Coupling
You should NEVER:
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A.
Back under a trailer at an angle
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B.
Inspect the fifth wheel
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C.
Use the parking brake
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D.
Tug-test the kingpin
Correct answer: A.
Backing at an angle can damage the kingpin or push the trailer sideways.
Question 21 of 25 · Coupling
What are landing gear used for?
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A.
Supporting the front of the trailer when uncoupled
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B.
Steering the trailer
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C.
Powering the trailer brakes
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D.
Lighting the trailer
Correct answer: A.
Landing gear holds up the trailer when it is not connected to a tractor.
Question 22 of 25 · Vehicle Dynamics
Which of these is true about the front trailer of a doubles or triples?
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A.
It is less likely to overturn
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B.
It is more stable
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C.
It is more likely to overturn than the rear trailer
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D.
It does not need brakes
Correct answer: A.
The front trailer in a combination is generally more stable than the rear trailer.
Question 23 of 25 · Cargo
Why is securement of cargo essential?
-
A.
To prevent the load from shifting
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B.
To prevent injury to others
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C.
To prevent damage to the vehicle
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D.
All of the above
Correct answer: D.
Securement protects the load, prevents shifts that affect handling, and protects others.
Question 24 of 25 · Inspection
Which is true about gladhand seals?
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A.
They should be replaced if cracked or damaged
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B.
They never need replacement
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C.
They are the same as electrical connections
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D.
They are always made of metal
Correct answer: A.
Replace damaged or worn rubber seals to keep air from leaking at the gladhands.
Question 25 of 25 · Vehicle Dynamics
Off-tracking is most pronounced in:
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A.
Single vehicles
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B.
Long combinations and curves
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C.
Empty trailers
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D.
Vehicles with disc brakes
Correct answer: B.
Longer wheelbases and tighter curves cause greater off-tracking.
About the Combination Vehicles Test
The Combination Vehicles test covers driving combination vehicles safely, combination vehicle air brakes, antilock brake systems, coupling and uncoupling, and inspecting a combination vehicle. Combination vehicles are usually heavier, longer, and require more driving skill than single commercial vehicles. They are also more likely to roll over and jackknife.
The California Department of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your California CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Coupling: 8 questions
- Vehicle Dynamics: 4 questions
- Inspection: 4 questions
- Skids: 3 questions
- Combination Air: 2 questions
- Cargo: 2 questions
- Operation: 1 question
- Following Distance: 1 question
How to use this practice test
- Read each question carefully. CDL questions are written precisely — small wording differences matter.
- Click "Show Answers & Explanations" only after answering every question. Don't peek mid-test.
- Read the explanation for every question, even ones you got right. The reasoning is more important than the answer.
- Repeat the test until you score 100%. The questions are deterministic per state, so you can track your improvement over multiple sessions.
- Move on to the other endorsement tests for California until you're ready for the official exam.
Tips specific to the Combination Vehicles test
Combination Vehicles questions cover off-tracking, jackknifing, coupling and uncoupling, the fifth wheel, kingpin, glad hands, landing gear, and the special air-brake considerations for tractor-trailer combinations. Expect detailed step-by-step coupling questions.