25 realistic Combination Vehicles practice questions for Oregon CDL applicants. Required for: Class A CDL (tractor-trailer combinations). Official test: 20 questions, 16 correct to pass.
Question 1 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 2 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 3 of 25 · Vehicle Dynamics
Which of these is true about driving combination vehicles?
-
A.
They are easier to handle than single vehicles
-
B.
They are more likely to roll over and jackknife
-
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 4 of 25 · Coupling
You should NEVER:
-
A.
Back under a trailer at an angle
-
B.
Inspect the fifth wheel
-
C.
Use the parking brake
-
D.
Tug-test the kingpin
Correct answer: A.
Backing at an angle can damage the kingpin or push the trailer sideways.
Question 5 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 6 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 7 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 8 of 25 · Backing
Which is correct about backing a tractor-trailer?
-
A.
Steer in the same direction you want the trailer to go
-
B.
Steer in the opposite direction you want the trailer to go
-
C.
Use the throttle to back
-
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 9 of 25 · Coupling
What is the proper position for the fifth wheel?
-
A.
Tilted down toward the rear of the tractor with jaws open
-
B.
Pointed straight up
-
C.
Locked and ready
-
D.
Removed for inspection
Correct answer: A.
Before coupling, the fifth wheel should tilt down toward the rear with the jaws open.
Question 10 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
-
C.
Apply trailer brakes during a normal stop
-
D.
Disconnect the trailer
Correct answer: A.
It protects the tractor air supply by closing if a major air loss occurs.
Question 11 of 25 · Inspection
What is the proper way to test the parking brakes after coupling?
-
A.
Apply trailer parking brake and try to gently pull forward
-
B.
Drive at normal speed
-
C.
Apply foot brake repeatedly
-
D.
Disconnect glad hands
Correct answer: A.
A gentle pull forward with parking brakes set confirms holding power.
Question 12 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 13 of 25 · Inspection
Which of these is not a part of the trailer's electrical system?
-
A.
Lights
-
B.
Brake control
-
C.
Power line cord (pigtail)
-
D.
Hydraulic pump
Correct answer: D.
Hydraulic pumps are not part of standard trailer electrical systems on highway combinations.
Question 14 of 25 · Skids
What is the result of a "trailer jackknife"?
-
A.
Trailer continues straight ahead
-
B.
Trailer swings out and tractor pivots
-
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 15 of 25 · Inspection
Air leaks during pre-trip can be detected by:
-
A.
Listening for hissing
-
B.
Watching the air gauges drop
-
C.
Visually inspecting hoses and fittings
-
D.
All of the above
Correct answer: D.
Use multiple methods — listening, watching gauges, and visual inspection — to detect leaks.
Question 16 of 25 · Following Distance
What is "rear-end collision" risk for combination vehicles?
-
A.
It is reduced when carrying long cargo
-
B.
They have a higher risk because of long stopping distances and rear blind spots
-
C.
They have no greater risk
-
D.
Only for empty rigs
Correct answer: B.
Long stopping distance and rear blind spots increase rear-end collision risk.
Question 17 of 25 · Bobtail
What happens if you bobtail (no trailer) and brake hard?
-
A.
You stop more quickly than loaded
-
B.
Drive wheels can lock and skid because there is little weight on them
-
C.
Vehicle handles like a loaded truck
-
D.
No special concerns
Correct answer: B.
Bobtailing leaves little weight on drive axles, increasing skid risk under hard braking.
Question 18 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 19 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 20 of 25 · Vehicle Dynamics
Why should you avoid sudden steering and braking with combinations?
-
A.
It wears tires faster
-
B.
It can cause jackknife or rollover
-
C.
It uses more fuel
-
D.
It scares passengers
Correct answer: B.
Sudden inputs can break traction and lead to jackknifing or rollovers.
Question 21 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
-
D.
Disconnected
Correct answer: A.
Air lines must be connected and supported off the deck so they don't snag or wear.
Question 22 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 23 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 24 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 25 of 25 · Skids
Tractor jackknife occurs when:
-
A.
Drive wheels lose traction and skid
-
B.
The trailer wheels lock
-
C.
The trailer slides forward
-
D.
Steering wheels lock
Correct answer: A.
Drive wheels skidding cause tractor jackknife; trailer wheels skidding cause trailer jackknife.
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 Oregon Driver and Motor Vehicle Services administers this knowledge test as part of its commercial driver license program. To earn the Combination Vehicles on your Oregon CDL, you need to score at least 16 out of 20 on the official version.
Topics covered on this practice test
- Coupling: 7 questions
- Vehicle Dynamics: 5 questions
- Skids: 4 questions
- Inspection: 3 questions
- Cargo: 1 question
- Backing: 1 question
- Combination Air: 1 question
- Mountain Driving: 1 question
- Following Distance: 1 question
- Bobtail: 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 Oregon 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.