25 realistic Combination Vehicles practice questions for Wisconsin CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 of 25 · Skids
Tractor jackknife occurs when:
-
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 2 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 3 of 25 · Combination Air
Trailer hand valve is used to:
-
A.
Test trailer brakes
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B.
Park the trailer
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C.
Bypass the foot valve
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D.
Drain trailer tanks
Correct answer: A.
Use the trailer hand valve only for testing — not for parking or normal stops.
Question 4 of 25 · Mountain Driving
When should you use lower gears?
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A.
On steep upgrades and downgrades
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B.
In flat terrain
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C.
In stop-and-go traffic only
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D.
Never in a combination vehicle
Correct answer: A.
Use lower gears on grades to maintain torque and engine braking.
Question 5 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 6 of 25 · Bobtail
What happens if you bobtail (no trailer) and brake hard?
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A.
You stop more quickly than loaded
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B.
Drive wheels can lock and skid because there is little weight on them
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C.
Vehicle handles like a loaded truck
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D.
No special concerns
Correct answer: B.
Bobtailing leaves little weight on drive axles, increasing skid risk under hard braking.
Question 7 of 25 · Inspection
Which is true about gladhand seals?
-
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 8 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 9 of 25 · Combination Air
What is glad hands?
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A.
Trailer doors
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B.
Couplers used to join air lines from the tractor to the trailer
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C.
Mirror brackets
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D.
Brake levers
Correct answer: B.
Glad hands connect the service and emergency air lines between tractor and trailer.
Question 10 of 25 · Vehicle Dynamics
Empty trucks have what kind of stopping distance compared to fully loaded ones?
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A.
Shorter
-
B.
Same
-
C.
Longer
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D.
Half
Correct answer: C.
Empty rigs have less traction on drive axles and require greater stopping distance.
Question 11 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 12 of 25 · Coupling
When uncoupling, what is the final step?
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A.
Lower the landing gear and disconnect electrical cord and air lines
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B.
Drive forward immediately
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C.
Set the parking brake on the tractor only
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D.
Engage the trailer brakes only
Correct answer: A.
After raising the fifth wheel jaws and pulling forward, disconnect lines and lower landing gear.
Question 13 of 25 · Skids
What should you do to recover from a trailer skid?
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A.
Apply more brake pressure
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B.
Release the brakes to allow trailer wheels to roll again
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C.
Steer hard right
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D.
Accelerate forward
Correct answer: B.
Release brakes to let trailer wheels roll, then steer to recover direction.
Question 14 of 25 · Vehicle Dynamics
What is "off-tracking"?
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A.
When the rear wheels follow a different path than the front wheels
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B.
When the trailer slides off the road
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C.
When the trailer is improperly loaded
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D.
A type of fifth wheel
Correct answer: A.
In turns, rear wheels travel a smaller arc than the front, causing off-tracking.
Question 15 of 25 · Skids
What is the result of a "trailer jackknife"?
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A.
Trailer continues straight ahead
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B.
Trailer swings out and tractor pivots
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C.
Trailer comes to a quick safe stop
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D.
Trailer disengages
Correct answer: B.
In a trailer jackknife, the trailer swings out, often into adjacent lanes.
Question 16 of 25 · Emergency Equipment
What are some common causes of vehicle fires?
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A.
Under-inflated tires and electrical short circuits
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B.
Improper use of flares
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C.
Cargo that catches fire from spilled fuel
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D.
All of the above
Correct answer: D.
All of these can cause vehicle fires. Pre-trip and en-route inspections reduce risk.
Question 17 of 25 · Inspection
Air leaks during pre-trip can be detected by:
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A.
Listening for hissing
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B.
Watching the air gauges drop
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C.
Visually inspecting hoses and fittings
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D.
All of the above
Correct answer: D.
Use multiple methods — listening, watching gauges, and visual inspection — to detect leaks.
Question 18 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 19 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 20 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 21 of 25 · Coupling
Which is true about pulling away after coupling?
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A.
Test that the kingpin is locked by gently pulling forward against the trailer brakes
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B.
Pull away as quickly as possible
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C.
Lower the landing gear before pulling away
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D.
Disconnect the air lines first
Correct answer: A.
A pull-test confirms the kingpin is locked before driving away.
Question 22 of 25 · Following Distance
How can you reduce risk of rear-end collisions?
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A.
Maintain safe following distances and watch for slowing traffic
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B.
Drive at the speed limit always
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C.
Use mirrors only at night
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D.
Avoid signaling
Correct answer: A.
Use safe following distances and watch ahead so you have time to slow down.
Question 23 of 25 · Coupling
What is the proper position for the fifth wheel?
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A.
Tilted down toward the rear of the tractor with jaws open
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B.
Pointed straight up
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C.
Locked and ready
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D.
Removed for inspection
Correct answer: A.
Before coupling, the fifth wheel should tilt down toward the rear with the jaws open.
Question 24 of 25 · Vehicle Dynamics
Why should you avoid sudden steering and braking with combinations?
-
A.
It wears tires faster
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B.
It can cause jackknife or rollover
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C.
It uses more fuel
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D.
It scares passengers
Correct answer: B.
Sudden inputs can break traction and lead to jackknifing or rollovers.
Question 25 of 25 · Speed Management
What is the most common cause of fatal crashes for combination vehicles?
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A.
Loss of control due to speed too fast for conditions
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B.
Engine failure
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C.
Tire blowouts
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D.
Mechanical defects only
Correct answer: A.
Driving too fast for conditions is the leading cause of serious crashes.
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 Wisconsin Division of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Wisconsin CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Skids: 4 questions
- Inspection: 4 questions
- Vehicle Dynamics: 4 questions
- Coupling: 4 questions
- Combination Air: 2 questions
- Mountain Driving: 1 question
- Cargo: 1 question
- Bobtail: 1 question
- Emergency Equipment: 1 question
- Operation: 1 question
- Following Distance: 1 question
- Speed Management: 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 Wisconsin 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.