25 realistic Combination Vehicles practice questions for Louisiana CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 of 25 · Mountain Driving
When should you use lower gears?
-
A.
On steep upgrades and downgrades
-
B.
In flat terrain
-
C.
In stop-and-go traffic only
-
D.
Never in a combination vehicle
Correct answer: A.
Use lower gears on grades to maintain torque and engine braking.
Question 2 of 25 · Coupling
When uncoupling, you should:
-
A.
Lower the landing gear before pulling the kingpin release
-
B.
Lift the trailer with the fifth wheel
-
C.
Release the parking brake
-
D.
Rev the engine
Correct answer: A.
Lower the landing gear so the trailer is supported before disconnecting the kingpin.
Question 3 of 25 · Cargo
How do you know the trailer is properly loaded?
-
A.
Cargo is centered, balanced, and properly secured
-
B.
Cargo extends beyond the trailer ends
-
C.
Cargo is stacked unevenly
-
D.
Cargo is on top of the cab
Correct answer: A.
Centered, balanced, and secured loads handle predictably.
Question 4 of 25 · Vehicle Dynamics
When you turn suddenly with a high center of gravity, the trailer can:
-
A.
Roll over
-
B.
Stop more quickly
-
C.
Track better
-
D.
Reduce fuel use
Correct answer: A.
High centers of gravity make trailers prone to rollover during sharp turns.
Question 5 of 25 · Coupling
Before backing under a trailer, you should:
-
A.
Make sure the trailer brakes are set and the trailer is at the correct height
-
B.
Disconnect the air lines
-
C.
Lower the landing gear
-
D.
Engage the parking brake
Correct answer: A.
Confirm trailer brakes are locked and trailer height matches the fifth wheel.
Question 6 of 25 · Skids
What can cause a trailer skid in a combination vehicle?
-
A.
Locked trailer wheels and over-application of brakes
-
B.
Light loads on the trailer
-
C.
Tight steering at low speed
-
D.
High pressure in steering tires
Correct answer: A.
Locked trailer wheels cause trailer skid; reduce brake pressure to recover.
Question 7 of 25 · Skids
What should you do to recover from a trailer skid?
-
A.
Apply more brake pressure
-
B.
Release the brakes to allow trailer wheels to roll again
-
C.
Steer hard right
-
D.
Accelerate forward
Correct answer: B.
Release brakes to let trailer wheels roll, then steer to recover direction.
Question 8 of 25 · Skids
What is "tractor jackknife"?
-
A.
Tractor drive wheels skid and the trailer pushes the tractor sideways
-
B.
Trailer wheels skid
-
C.
Steering wheels skid
-
D.
Engine fails
Correct answer: A.
When drive wheels skid, the trailer can push the tractor sideways into a jackknife.
Question 9 of 25 · Combination Air
Trailer hand valve is used to:
-
A.
Test trailer brakes
-
B.
Park the trailer
-
C.
Bypass the foot valve
-
D.
Drain trailer tanks
Correct answer: A.
Use the trailer hand valve only for testing — not for parking or normal stops.
Question 10 of 25 · Vehicle Dynamics
Off-tracking is most pronounced in:
-
A.
Single vehicles
-
B.
Long combinations and curves
-
C.
Empty trailers
-
D.
Vehicles with disc brakes
Correct answer: B.
Longer wheelbases and tighter curves cause greater off-tracking.
Question 11 of 25 · Vehicle Dynamics
What's the safest way to handle a tight turn with a long combination?
-
A.
Take it wide using both lanes if necessary
-
B.
Drive as fast as possible to maintain momentum
-
C.
Use the trailer hand valve
-
D.
Make a tight turn
Correct answer: A.
Take wider turns to avoid hitting curbs or other vehicles due to off-tracking.
Question 12 of 25 · Coupling
What does a "low coupling" condition look like?
-
A.
Trailer is too high above the fifth wheel
-
B.
Trailer is at the right height
-
C.
Trailer is too low and tractor frame can hit the trailer
-
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 13 of 25 · Inspection
Which is true about gladhand seals?
-
A.
They should be replaced if cracked or damaged
-
B.
They never need replacement
-
C.
They are the same as electrical connections
-
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 14 of 25 · Cargo
What can cause a high center of gravity?
-
A.
Loading cargo too low
-
B.
Loading cargo too high or unevenly
-
C.
Driving too slowly
-
D.
Empty trailers
Correct answer: B.
Stacking cargo too high or loading unevenly raises the center of gravity and rollover risk.
Question 15 of 25 · Skids
How can drivers avoid jackknifing?
-
A.
Brake gently and look ahead
-
B.
Adjust speed for road and weather
-
C.
Use ABS where equipped
-
D.
All of the above
Correct answer: D.
Smooth braking, appropriate speed, and ABS all reduce jackknife risk.
Question 16 of 25 · Coupling
When coupling, what should you do after the fifth wheel locks onto the kingpin?
-
A.
Pull the tractor forward gently to make sure the kingpin is locked
-
B.
Disconnect the air lines
-
C.
Drive away immediately
-
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 17 of 25 · Coupling
What is the fifth wheel?
-
A.
A spare wheel
-
B.
A coupling device that connects the tractor to the trailer
-
C.
A device on the trailer to support cargo
-
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 18 of 25 · Combination Air
Trailer brakes are required to be:
-
A.
Adjusted properly and matched to tractor brakes
-
B.
Stronger than tractor brakes
-
C.
Disengaged on level roads
-
D.
Off when empty
Correct answer: A.
Trailer brakes must be in proper adjustment and balance with tractor brakes.
Question 19 of 25 · Speed Management
What is the most common cause of fatal crashes for combination vehicles?
-
A.
Loss of control due to speed too fast for conditions
-
B.
Engine failure
-
C.
Tire blowouts
-
D.
Mechanical defects only
Correct answer: A.
Driving too fast for conditions is the leading cause of serious crashes.
Question 20 of 25 · Coupling
How can you keep a stiff coupling system from causing problems?
-
A.
Lubricate the fifth wheel
-
B.
Avoid backing under fast
-
C.
Inspect mounting bolts
-
D.
All of the above
Correct answer: D.
Lubricate, back slowly, and inspect mounting bolts to keep the coupling working safely.
Question 21 of 25 · Coupling
What are landing gear used for?
-
A.
Supporting the front of the trailer when uncoupled
-
B.
Steering the trailer
-
C.
Powering the trailer brakes
-
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 · Operation
Which of these is most important when driving with a trailer?
-
A.
Use the engine retarder constantly
-
B.
Use proper braking and signaling
-
C.
Drive at maximum speed limits
-
D.
Skip pre-trip checks if running late
Correct answer: B.
Proper braking and clear signaling are essential to safe combination driving.
Question 23 of 25 · Skids
Which is the most common cause of trailer skid?
-
A.
Driving too fast for conditions
-
B.
Locking the rear trailer wheels by overbraking
-
C.
Worn brake shoes
-
D.
Too much trailer weight
Correct answer: B.
Trailer skids most often occur when rear trailer wheels lock during braking.
Question 24 of 25 · Inspection
When checking the trailer air supply, you should:
-
A.
Charge the trailer with air, then disconnect the supply hose to test trailer emergency brakes
-
B.
Pump the brakes
-
C.
Disconnect the trailer power cord
-
D.
Open the trailer service line manually
Correct answer: A.
Disconnecting the supply line tests that the trailer emergency brakes apply automatically.
Question 25 of 25 · Combination Air
What is glad hands?
-
A.
Trailer doors
-
B.
Couplers used to join air lines from the tractor to the trailer
-
C.
Mirror brackets
-
D.
Brake levers
Correct answer: B.
Glad hands connect the service and emergency air lines between tractor and trailer.
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 Louisiana Office of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Louisiana CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Coupling: 7 questions
- Skids: 5 questions
- Vehicle Dynamics: 3 questions
- Combination Air: 3 questions
- Cargo: 2 questions
- Inspection: 2 questions
- Mountain Driving: 1 question
- Speed Management: 1 question
- Operation: 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 Louisiana 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.