25 realistic Combination Vehicles practice questions for Michigan CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 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 2 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 3 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 4 of 25 · Combination Air
When the trailer breaks away or loses air pressure, the trailer brakes should:
-
A.
Release
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B.
Apply automatically
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C.
Vibrate
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D.
Disengage
Correct answer: B.
A loss of air should automatically apply the trailer brakes via the emergency system.
Question 5 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 6 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 7 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 8 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 9 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 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 · 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 12 of 25 · Vehicle Dynamics
Empty trucks have what kind of stopping distance compared to fully loaded ones?
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A.
Shorter
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B.
Same
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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 13 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 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 · 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 16 of 25 · Backing
Which is correct about backing a tractor-trailer?
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A.
Steer in the same direction you want the trailer to go
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B.
Steer in the opposite direction you want the trailer to go
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C.
Use the throttle to back
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D.
Back as fast as possible
Correct answer: B.
When backing, turn the steering wheel opposite to the direction you want the trailer to move.
Question 17 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 18 of 25 · Skids
How can drivers avoid jackknifing?
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A.
Brake gently and look ahead
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B.
Adjust speed for road and weather
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C.
Use ABS where equipped
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D.
All of the above
Correct answer: D.
Smooth braking, appropriate speed, and ABS all reduce jackknife risk.
Question 19 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.
Question 20 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 21 of 25 · Combination Air
Trailer hand valve is used to:
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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 22 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 23 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 24 of 25 · Coupling
When uncoupling, you should:
-
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 25 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.
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 Michigan Secretary of State — Driver Services administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Michigan CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Coupling: 6 questions
- Combination Air: 4 questions
- Skids: 4 questions
- Inspection: 3 questions
- Vehicle Dynamics: 3 questions
- Emergency Equipment: 1 question
- Following Distance: 1 question
- Bobtail: 1 question
- Backing: 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 Michigan 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.