25 realistic Combination Vehicles practice questions for Maine 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 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 2 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 3 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 4 of 25 · Inspection
When inspecting your trailer's wheels, what should you look for?
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A.
Loose or missing nuts
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B.
Cracked or broken wheel rims
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C.
Bent or broken studs
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D.
All of the above
Correct answer: D.
Inspect for loose nuts, cracks, bent studs, and other defects on every pre-trip.
Question 5 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 6 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 7 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 8 of 25 · Inspection
What is the proper way to test the parking brakes after coupling?
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A.
Apply trailer parking brake and try to gently pull forward
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B.
Drive at normal speed
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C.
Apply foot brake repeatedly
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D.
Disconnect glad hands
Correct answer: A.
A gentle pull forward with parking brakes set confirms holding power.
Question 9 of 25 · Inspection
You should inspect the rear of the trailer for:
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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 · 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 11 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 12 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.
Question 13 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 14 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 15 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 16 of 25 · Vehicle Dynamics
When you turn suddenly with a high center of gravity, the trailer can:
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A.
Roll over
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B.
Stop more quickly
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C.
Track better
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D.
Reduce fuel use
Correct answer: A.
High centers of gravity make trailers prone to rollover during sharp turns.
Question 17 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 18 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 19 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 20 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 21 of 25 · Coupling
How can you keep a stiff coupling system from causing problems?
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A.
Lubricate the fifth wheel
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B.
Avoid backing under fast
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C.
Inspect mounting bolts
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D.
All of the above
Correct answer: D.
Lubricate, back slowly, and inspect mounting bolts to keep the coupling working safely.
Question 22 of 25 · Cargo
How do you know the trailer is properly loaded?
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A.
Cargo is centered, balanced, and properly secured
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B.
Cargo extends beyond the trailer ends
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C.
Cargo is stacked unevenly
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D.
Cargo is on top of the cab
Correct answer: A.
Centered, balanced, and secured loads handle predictably.
Question 23 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 24 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 25 of 25 · Skids
What can cause a trailer skid in a combination vehicle?
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A.
Locked trailer wheels and over-application of brakes
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B.
Light loads on the trailer
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C.
Tight steering at low speed
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D.
High pressure in steering tires
Correct answer: A.
Locked trailer wheels cause trailer skid; reduce brake pressure to recover.
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 Maine Bureau of Motor Vehicles administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Maine CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Inspection: 6 questions
- Vehicle Dynamics: 4 questions
- Skids: 4 questions
- Coupling: 4 questions
- Cargo: 2 questions
- Following Distance: 1 question
- Mountain Driving: 1 question
- Emergency Equipment: 1 question
- Operation: 1 question
- Combination Air: 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 Maine 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.