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Oregon Combination Vehicles CDL Practice Test

Below are 25 exam-style questions for the Oregon Combination Vehicles CDL knowledge test, modeled on the FMCSA-aligned content used by the Oregon Driver and Motor Vehicle Services. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.
Question 1 of 25
Trailer parking brakes are released:
  • A By pushing in the red trailer-air-supply valve
  • B By the trailer hand valve
  • C By setting the red trailer-air-supply valve
  • D By pulling out the red trailer-air-supply valve
Correct answer: A
Pushing in the red knob charges the trailer brakes and releases the spring brakes.
Question 2 of 25
When you uncouple a trailer with cargo on it, you should:
  • A Lower the landing gear all the way until firmly on the ground, then a few extra cranks
  • B Use blocks instead
  • C Leave the gear up
  • D Raise the gear partway
Correct answer: A
Make sure the gear takes the full weight before pulling out from under.
Question 3 of 25
If you cross the air lines (service to emergency and vice versa) when coupling:
  • A Nothing will happen
  • B The horn will sound
  • C The trailer brakes will be locked on
  • D You will notice immediately because trailer brakes will not work properly
Correct answer: D
Crossed glad hands often produce no air flow to brake chambers and incorrect brake operation; you should notice on the brake test.
Question 4 of 25
If you are pulling two trailers, the heavier trailer should be:
  • A Loaded last
  • B Last
  • C Either position is fine
  • D First (closest to the tractor)
Correct answer: D
Heavier trailer first reduces the rear-trailer crack-the-whip effect.
Question 5 of 25
A tractor jackknife happens when:
  • A The fifth wheel disengages
  • B The drive wheels lose traction and the tractor begins to slide
  • C The tractor parking brake fails
  • D The trailer is too heavy
Correct answer: B
A drive-wheel skid causes the tractor to swing into the trailer at an angle.
Question 6 of 25
The trailer hand valve operates:
  • A The parking brake
  • B Both tractor and trailer brakes simultaneously
  • C The tractor service brakes only
  • D The trailer service brakes only
Correct answer: D
The hand valve applies only the trailer service brakes. It is for testing — not for parking or routine use.
Question 7 of 25
The fifth-wheel locking lever should be:
  • A Released and visible after coupling
  • B Removed before driving
  • C Locked and the safety latch in place after coupling
  • D Tied with rope
Correct answer: C
After backing under, the locking jaws must close around the kingpin and the safety latch must be in place.
Question 8 of 25
When you turn a combination vehicle right at an intersection, you should:
  • A Keep the cab close to the curb and swing the front out so following cars cannot squeeze beside you on the right
  • B Swing wide to the right first to avoid hitting the curb
  • C Swing left then right
  • D Stop in the middle of the turn
Correct answer: A
Hugging the right side of the turn lane prevents another vehicle from squeezing in next to you and getting clipped by the trailer.
Question 9 of 25
Most rear-end collisions caused by combination vehicles result from:
  • A Engine failure
  • B Driving too fast for conditions and/or too closely
  • C Worn out tires
  • D Cargo movement
Correct answer: B
Speed and following distance dominate the causes. Increase cushion and slow down.
Question 10 of 25
Before pulling the kingpin release lever to uncouple, you must:
  • A Lower the trailer landing gear and chock the trailer wheels
  • B Drain the air tanks
  • C Honk the horn
  • D Disconnect the electrical line first
Correct answer: A
Always lower the landing gear and chock the trailer so it cannot move once you pull out from under it.
Question 11 of 25
When coupling a tractor to a semitrailer, the trailer should be at:
  • A A height that requires the tractor to drop down to fit
  • B Whatever height it happens to be
  • C Maximum legal height
  • D A height where the tractor will lift the trailer slightly when backing under
Correct answer: D
The trailer should be slightly lower than the fifth wheel so backing in lifts the trailer.
Question 12 of 25
A "trailer skid" usually starts because:
  • A A wheel bearing fails
  • B The tractor brakes lock up
  • C The fifth wheel breaks
  • D The trailer brakes lock up
Correct answer: D
Locking the trailer brakes is the most common cause of a trailer skid (jackknife).
Question 13 of 25
The proper sequence for uncoupling is generally:
  • A Pull tractor away first, then disconnect lines
  • B Lower landing gear, disconnect lines, release fifth wheel, pull tractor away
  • C Release fifth wheel first, then connect lines
  • D No specific order is required
Correct answer: B
Lower the landing gear, chock the wheels, disconnect air and electrical lines and stow them, release the fifth wheel, then slowly pull the tractor forward.
Question 14 of 25
You should inspect a combination vehicle for:
  • A All of the above
  • B Loose or missing fifth-wheel mounting bolts
  • C Misalignment between tractor and trailer
  • D Cracks in the kingpin
Correct answer: A
All three are pre-trip combination-vehicle items.
Question 15 of 25
Tracking refers to:
  • A The fuel mileage
  • B Lane positioning at intersections
  • C Cargo placement
  • D The trailer following the same path as the tractor in a straight line
Correct answer: D
Tracking is how well the trailer follows the tractor; misalignment can indicate suspension or tire problems.
Question 16 of 25
The trailer hand valve should NOT be used to:
  • A Apply trailer brakes momentarily
  • B Test the trailer brakes
  • C Both for parking and to prevent jackknife
  • D Hold the vehicle when parking
Correct answer: C
Don't use it to park (it can leak off) or to prevent a jackknife (it locks the trailer wheels and worsens the skid).
Question 17 of 25
When backing a tractor-trailer, you should:
  • A Back without using mirrors
  • B Back to the left whenever possible because you can see better
  • C Always back to the right
  • D Back as fast as practical
Correct answer: B
Backing to the driver's side gives the best view of the trailer. Always GOAL — Get Out And Look — before and during.
Question 18 of 25
A safe combination-vehicle following distance is at least:
  • A No specific rule
  • B Two car lengths
  • C A vehicle length
  • D One second per 10 feet of vehicle length below 40 mph, plus one extra second above 40 mph
Correct answer: D
A 60-ft combination needs at least 6 seconds under 40 mph, 7 seconds above 40 mph.
Question 19 of 25
The seven-pin connector on a tractor-trailer carries:
  • A Hydraulic fluid
  • B Electrical power for trailer lights and ABS
  • C Fuel
  • D Air for the brakes
Correct answer: B
The seven-pin (or older five-pin) is electrical, supplying lights, brake-light signal, and ABS.
Question 20 of 25
A skid is most likely to result in a jackknife if:
  • A The drive wheels lock and the trailer pushes the tractor sideways
  • B You are driving slowly
  • C The trailer wheels lock briefly
  • D The brakes are released gently
Correct answer: A
Drive-wheel lockup is the classic jackknife cause.
Question 21 of 25
A heavy combination vehicle in a curve is most likely to:
  • A Lose engine power
  • B Spin out
  • C Stop suddenly
  • D Roll over before sliding
Correct answer: D
Loaded trailers reach the rollover threshold before they slide. Slow before the curve.
Question 22 of 25
A combination vehicle with empty trailers:
  • A May actually take longer to stop because brakes are designed for the loaded weight
  • B Stops faster than when loaded
  • C Stops only with parking brake
  • D Stops in the same distance
Correct answer: A
Empty trailers can lock up easily and skid, which counterintuitively increases stopping distance.
Question 23 of 25
Trailer ABS uses:
  • A A separate compressor
  • B Hydraulic brakes
  • C Hand valves
  • D Sensors at each wheel that release brake pressure when wheel lockup is detected
Correct answer: D
Wheel-speed sensors trigger valves to release pressure when lockup is detected.
Question 24 of 25
After connecting the air lines, before pulling the tractor away, you must:
  • A Drain the wet tank
  • B Pump the brakes 10 times
  • C Drive away immediately
  • D Charge the trailer brakes by setting the trailer air supply control
Correct answer: D
After connecting, charge the trailer system and verify brake operation.
Question 25 of 25
Which of the following can damage a fifth wheel?
  • A Failure to grease
  • B Backing too fast
  • C All of the above
  • D Coupling with the trailer too high
Correct answer: C
All three: high trailer skips the jaws, fast backing impacts hardware, and lack of lubrication accelerates wear.

Study tips for the Oregon Combination Vehicles exam

The Combination Vehicles portion of the Oregon CDL exam is graded out of the bank of questions the Oregon Driver and Motor Vehicle Services draws from each year. While the exact bank is not published, every question is sourced from the Combination Vehicles chapter of the Oregon CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Oregon handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Combination Vehicles.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Oregon Driver and Motor Vehicle Services will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Combination Vehicles exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Oregon General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Combination Vehicles study guide and the matching chapter in the official Oregon CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Oregon Driver and Motor Vehicle Services office.

Already comfortable with this endorsement? Drill another: OR General Knowledge · OR Air Brakes · OR Hazardous Materials · OR Passenger · OR School Bus · OR Tank Vehicle · OR Doubles / Triples

New to the CDL process in Oregon? Read How to apply for a CDL in Oregon for the document checklist and step-by-step timeline.