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CDL Combination Vehicles Practice Test 2026

You take the combination vehicles test to drive a tractor-semitrailer or other Class A combination. These questions cover driving combinations safely, trailer air brakes, the coupling steps and the extra inspection checks.

  • Commercial vehicle
  • United States
  • 70 questions
  • Checked October 10, 2026

Quick answer

Pass mark: 80% correct; the number of questions varies by state (20 in Washington, 30 in Utah). It is run by Your state driver licensing agency, under federal rules set by FMCSA (49 CFR Part 383). Practise here for free with 70 questions, each with the answer and an explanation. Checked against official sources on October 10, 2026.

Read before you practiseStart with the CDL Combination Vehicles Study Guide: plain-language notes, diagrams and the numbers to remember.

  1. Question 1 of 25

    What causes more than half of truck driver deaths in crashes?
    Show answer

    Answer: C. Truck rollovers

    More than half of truck driver deaths in crashes are the result of truck rollovers.

  2. Question 2 of 25

    Compared with an empty rig, how much more likely is a fully loaded rig to roll over in a crash?
    Show answer

    Answer: A. About 10 times more likely

    Fully loaded rigs are ten times more likely to roll over in a crash than empty rigs.

  3. Question 3 of 25

    How should you load cargo to help prevent a rollover?
    Show answer

    Answer: A. As low as possible, centered and spread out

    Keep the center of gravity low, and keep cargo centered so the trailer does not lean.

  4. Question 4 of 25

    Which driving habit helps prevent rollovers?
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    Answer: B. Going slowly around corners and ramps

    Drive slowly in turns and on ramps, and avoid quick lane changes, especially when fully loaded.

  5. Question 5 of 25

    What is rearward amplification?
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    Answer: C. The crack-the-whip effect that can tip over a trailer

    Rearward amplification makes the rear trailer swing more than the tractor in a sudden move. It can tip the trailer over.

  6. Question 6 of 25

    Which part of a combination is most likely to turn over in a quick lane change?
    Show answer

    Answer: B. The last trailer

    Because of rearward amplification, the rearmost trailer is the most likely to turn over.

  7. Question 7 of 25

    A combination has a rearward amplification of 2.0. What does that mean?
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    Answer: A. The rear trailer is twice as likely to tip as the tractor

    A rearward amplification of 2.0 means the rear trailer is twice as likely to turn over as the tractor.

  8. Question 8 of 25

    How should you steer a combination vehicle?
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    Answer: B. Gently and smoothly

    Sudden steering can tip a trailer over. Steer gently and smoothly.

  9. Question 9 of 25

    Compared with a loaded combination, how does an empty combination behave when you brake?
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    Answer: C. It may take longer to stop, as wheels lock easily

    Empty rigs have stiff springs and strong brakes but poor traction, so wheels lock easily and stopping takes longer.

  10. Question 10 of 25

    What is a bobtail tractor?
    Show answer

    Answer: D. A tractor driving without a semitrailer

    A bobtail is a tractor without a trailer. It can be hard to stop smoothly and may take longer to stop than a loaded rig.

  11. Question 11 of 25

    Which trailers are most likely to get stuck on a raised railroad crossing?
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    Answer: B. Low-slung units like lowboys, car carriers and moving vans

    Trailers with low underneath clearance can hang up on raised crossings.

  12. Question 12 of 25

    What is a trailer jackknife?
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    Answer: A. When locked trailer wheels let the trailer swing around

    A trailer jackknife happens when the trailer wheels lock and the trailer swings out. It is more likely with an empty or light trailer.

  13. Question 13 of 25

    How can you spot a trailer skid early?
    Show answer

    Answer: D. Check your mirrors when you brake hard

    Check the mirrors any time you brake hard. Once the trailer is out of your lane, a jackknife is hard to stop.

  14. Question 14 of 25

    Your trailer starts to skid sideways because its wheels are locked. What should you do?
    Show answer

    Answer: B. Release the brakes to get traction back

    Release the brakes so the trailer wheels grip again. Do not use the trailer hand brake, because the trailer brakes caused the skid.

  15. Question 15 of 25

    What is offtracking?
    123
    Show answer

    Answer: D. Rear wheels taking a shorter path than the front in a turn

    In turns, the rear wheels cut inside the path of the front wheels. Longer vehicles offtrack more.

  16. Question 16 of 25

    The diagram shows a right turn. Which wheels offtrack the most?
    123
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    Answer: C. The rear wheels of the last trailer

    The rear wheels of the rearmost trailer offtrack the most.

  17. Question 17 of 25

    The diagram shows a correct right turn. What is this "button hook" method?
    123
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    Answer: D. Keep the rear near the curb, then turn wide as you finish

    The button hook turn stops cars from passing you on the right. The jug-handle turn, swinging left first, is wrong.

  18. Question 18 of 25

    You are backing a trailer and want it to move to the right. Which way do you turn the top of the steering wheel?
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    Answer: B. To the left

    When backing a trailer, turn the wheel the opposite way from where you want the trailer to go.

  19. Question 19 of 25

    You are backing a trailer and it starts to turn the way you want. What should you do next?
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    Answer: D. Turn the wheel the other way to follow it

    Once the trailer starts to turn, turn the wheel the other way so the tractor follows the trailer.

  20. Question 20 of 25

    If you must back a trailer on a curve, which way should you back?
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    Answer: D. Toward the driver's side

    Backing toward the driver's side lets you see the trailer better.

  21. Question 21 of 25

    Your trailer drifts while you back up. How do you correct it?
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    Answer: C. Turn the top of the wheel toward the drift

    Correct drift right away by turning the top of the wheel toward the drift. Back slowly so you can correct early.

  22. Question 22 of 25

    While backing a trailer, you get out of position. What should you do?
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    Answer: D. Pull forward (a pull-up) to reposition

    Use pull-ups to get back into position when needed.

  23. Question 23 of 25

    Your combination is 70 feet long and you are driving at 55 mph. What following distance should you keep?
    123
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    Answer: B. At least 8 seconds

    Allow 1 second per 10 feet of length (7 seconds) and add 1 second above 40 mph.

  24. Question 24 of 25

    What is the trailer hand valve (trolley valve) for?
    Show answer

    Answer: A. Testing the trailer brakes

    Use the trailer hand valve only to test the trailer brakes. Do not use it while driving or to park.

  25. Question 25 of 25

    Why should you use the foot brake rather than the trailer hand valve for normal stops?
    Show answer

    Answer: D. The hand valve brakes only the trailer, so it may skid

    Using the trailer brakes alone can make the trailer skid. The foot brake applies air to all wheels.

What to know before the test

  • Federal rules set the passing score for every CDL knowledge test: you must answer at least 80% of the questions correctly.
  • The number of questions varies by state. Washington's combination test has 20 questions, so you need 16 correct.
  • Utah's combination test has 30 questions, so at 80% you need 24 correct.
  • Class A covers combinations with a gross combination weight rating of 26,001 pounds or more when the towed vehicle is rated over 10,000 pounds.
  • If your Class A skills test vehicle is joined by a pintle hook instead of a fifth wheel, your CDL will be restricted from fifth-wheel tractor-trailers.
  • Trailers and converter dollies built on or after March 1, 1998 must have antilock brakes, with a yellow warning lamp on the left side.

Frequently asked questions

Who needs the combination vehicles test?

Anyone applying for a Class A CDL to drive a tractor-trailer or other heavy combination takes the combination vehicles knowledge test.

How many questions are on the combination test?

It depends on your state. Washington uses 20 questions and Utah uses 30. Either way, you need 80% to pass.

What is the most important coupling check?

Make sure there is no space between the upper and lower fifth wheel, the locking jaws are closed around the shank of the kingpin, and the locking lever is in the lock position with the safety latch over it.

What is the trailer hand valve for?

Only for testing the trailer brakes. Do not use it for normal stops or for parking.

Sources

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