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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.

  • 商用车辆
  • 美国
  • 70道题
  • 核对于2026年10月10日

快速解答

及格线：80% correct; the number of questions varies by state (20 in Washington, 30 in Utah)。 主办机构：Your state driver licensing agency, under federal rules set by FMCSA (49 CFR Part 383)。 在这里免费练习70道题，每道题都附有答案和解释。 已于2026年10月10日根据官方资料核对。

练习前先阅读先阅读《CDL Combination Vehicles Study Guide》：通俗易懂的笔记、图解和需要牢记的数字。

  1. 第1题，共25题

    What causes more than half of truck driver deaths in crashes?
    显示答案

    答案: C. Truck rollovers

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

  2. 第2题，共25题

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

    答案: A. About 10 times more likely

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

  3. 第3题，共25题

    How should you load cargo to help prevent a rollover?
    显示答案

    答案: 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. 第4题，共25题

    Which driving habit helps prevent rollovers?
    显示答案

    答案: B. Going slowly around corners and ramps

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

  5. 第5题，共25题

    What is rearward amplification?
    显示答案

    答案: 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. 第6题，共25题

    Which part of a combination is most likely to turn over in a quick lane change?
    显示答案

    答案: B. The last trailer

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

  7. 第7题，共25题

    A combination has a rearward amplification of 2.0. What does that mean?
    显示答案

    答案: 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. 第8题，共25题

    How should you steer a combination vehicle?
    显示答案

    答案: B. Gently and smoothly

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

  9. 第9题，共25题

    Compared with a loaded combination, how does an empty combination behave when you brake?
    显示答案

    答案: 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. 第10题，共25题

    What is a bobtail tractor?
    显示答案

    答案: 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. 第11题，共25题

    Which trailers are most likely to get stuck on a raised railroad crossing?
    显示答案

    答案: B. Low-slung units like lowboys, car carriers and moving vans

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

  12. 第12题，共25题

    What is a trailer jackknife?
    显示答案

    答案: 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. 第13题，共25题

    How can you spot a trailer skid early?
    显示答案

    答案: 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. 第14题，共25题

    Your trailer starts to skid sideways because its wheels are locked. What should you do?
    显示答案

    答案: 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. 第15题，共25题

    What is offtracking?
    123
    显示答案

    答案: 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. 第16题，共25题

    The diagram shows a right turn. Which wheels offtrack the most?
    123
    显示答案

    答案: C. The rear wheels of the last trailer

    The rear wheels of the rearmost trailer offtrack the most.

  17. 第17题，共25题

    The diagram shows a correct right turn. What is this "button hook" method?
    123
    显示答案

    答案: 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. 第18题，共25题

    You are backing a trailer and want it to move to the right. Which way do you turn the top of the steering wheel?
    显示答案

    答案: B. To the left

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

  19. 第19题，共25题

    You are backing a trailer and it starts to turn the way you want. What should you do next?
    显示答案

    答案: 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. 第20题，共25题

    If you must back a trailer on a curve, which way should you back?
    显示答案

    答案: D. Toward the driver's side

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

  21. 第21题，共25题

    Your trailer drifts while you back up. How do you correct it?
    显示答案

    答案: 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. 第22题，共25题

    While backing a trailer, you get out of position. What should you do?
    显示答案

    答案: D. Pull forward (a pull-up) to reposition

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

  23. 第23题，共25题

    Your combination is 70 feet long and you are driving at 55 mph. What following distance should you keep?
    123
    显示答案

    答案: B. At least 8 seconds

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

  24. 第24题，共25题

    What is the trailer hand valve (trolley valve) for?
    显示答案

    答案: 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. 第25题，共25题

    Why should you use the foot brake rather than the trailer hand valve for normal stops?
    显示答案

    答案: 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.

考前须知

  • 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.

常见问题

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.

资料来源

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