25 realistic Combination Vehicles practice questions for Washington CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 of 25 · Inspection
You should inspect the rear of the trailer for:
-
A.
Cracked or missing lights
-
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 2 of 25 · Inspection
Air leaks during pre-trip can be detected by:
-
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 3 of 25 · Combination Air
When the trailer breaks away or loses air pressure, the trailer brakes should:
-
A.
Release
-
B.
Apply automatically
-
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 4 of 25 · Inspection
When should you check trailer brakes during operation?
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A.
First few miles after coupling
-
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 5 of 25 · Combination Air
What should the tractor protection valve do?
-
A.
Keep tractor air supply if trailer breaks away or develops a major leak
-
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 · 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 7 of 25 · Skids
What can cause a trailer skid in a combination vehicle?
-
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.
Question 8 of 25 · Skids
What should you do to recover from a trailer skid?
-
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 9 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
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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 10 of 25 · Coupling
Which is true about pulling away after coupling?
-
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 11 of 25 · Mountain Driving
When should you use lower gears?
-
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 · Skids
How can drivers avoid jackknifing?
-
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 13 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 14 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
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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 · Vehicle Dynamics
Empty trucks have what kind of stopping distance compared to fully loaded ones?
-
A.
Shorter
-
B.
Same
-
C.
Longer
-
D.
Half
Correct answer: C.
Empty rigs have less traction on drive axles and require greater stopping distance.
Question 16 of 25 · Coupling
What are landing gear used for?
-
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 17 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 18 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
-
D.
Steering wheels lock
Correct answer: A.
Drive wheels skidding cause tractor jackknife; trailer wheels skidding cause trailer jackknife.
Question 19 of 25 · Vehicle Dynamics
When you turn suddenly with a high center of gravity, the trailer can:
-
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 20 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
-
D.
Trailer disengages
Correct answer: B.
In a trailer jackknife, the trailer swings out, often into adjacent lanes.
Question 21 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
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C.
Worn brake shoes
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D.
Too much trailer weight
Correct answer: B.
Trailer skids most often occur when rear trailer wheels lock during braking.
Question 22 of 25 · Vehicle Dynamics
Which of these is true about driving combination vehicles?
-
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
-
D.
They need fewer mirrors
Correct answer: B.
Combination vehicles require more skill and are more prone to rollovers and jackknives.
Question 23 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
-
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 24 of 25 · Emergency Equipment
What are some common causes of vehicle fires?
-
A.
Under-inflated tires and electrical short circuits
-
B.
Improper use of flares
-
C.
Cargo that catches fire from spilled fuel
-
D.
All of the above
Correct answer: D.
All of these can cause vehicle fires. Pre-trip and en-route inspections reduce risk.
Question 25 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
-
B.
Coiled tightly on top of the trailer
-
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.
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 Washington Department of Licensing administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Washington CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Skids: 6 questions
- Coupling: 5 questions
- Vehicle Dynamics: 4 questions
- Inspection: 3 questions
- Combination Air: 3 questions
- Cargo: 1 question
- Mountain Driving: 1 question
- Following Distance: 1 question
- Emergency Equipment: 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 Washington 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.