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CDL Doubles and Triples Practice Test 2026

The doubles/triples (T) endorsement lets you pull two or three trailers. These questions cover the extra rollover risk, coupling and uncoupling with a converter dolly, shut-off valve positions and the air brake checks.

  • 商用车辆
  • 美国
  • 50道题
  • 核对于2026年10月10日

快速解答

官方考试共有20道题。 及格线：Varies by state; usually 20 questions, with 16 correct needed (80%)。 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50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 Doubles and Triples 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

    Compared with other combinations, how likely are doubles and triples to turn over?
    显示答案

    答案: D. More likely

    Doubles and triples are more likely to turn over than other combination vehicles.

  2. 第2题，共25题

    Which trailer in a double or triple is most likely to turn over?
    显示答案

    答案: D. The last trailer

    Because of the crack-the-whip effect, the last trailer is the most likely to turn over.

  3. 第3题，共25题

    Compared with a five-axle tractor-semitrailer, how much more easily can the last trailer of a triple roll over?
    显示答案

    答案: A. About 3.5 times as easily

    Triples have the highest rearward amplification. The last trailer can roll about 3.5 times as easily.

  4. 第4题，共25题

    A speed that is safe for a single trailer on a curve is not always safe for doubles. Why?
    显示答案

    答案: D. Doubles and triples roll over more easily

    A speed that is fine for a straight truck or single trailer may be too fast for doubles or triples.

  5. 第5题，共25题

    What is the crack-the-whip effect?
    显示答案

    答案: D. A quick steering move swings the rear trailer much more

    Sudden steering is amplified toward the back of the rig. This rearward amplification can tip over the last trailer.

  6. 第6题，共25题

    Why do doubles and triples need extra care in the pre-trip inspection?
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    显示答案

    答案: C. They have more critical parts to check

    With two or three trailers, there are more parts that must be checked.

  7. 第7题，共25题

    Why should you look far ahead when pulling doubles or triples?
    显示答案

    答案: C. So you can slow down or change lanes gradually

    Drive very smoothly to avoid rollover or jackknife. Looking far ahead gives you time for gradual changes.

  8. 第8题，共25题

    How should your following distance compare when pulling doubles or triples?
    显示答案

    答案: A. Allow more following distance

    Doubles and triples are longer and cannot turn or stop suddenly, so leave more space ahead.

  9. 第9题，共25题

    Why are doubles and triples more likely to skid in bad weather?
    显示答案

    答案: B. Greater length and more dead axles mean less traction

    Be especially careful on slippery roads and in mountains. Length and extra axles raise the risk of skids.

  10. 第10题，共25题

    What should you avoid when parking doubles or triples?
    显示答案

    答案: A. A spot you cannot pull straight out of

    Plan your parking so you can pull straight through and avoid a long, difficult way out.

  11. 第11题，共25题

    Converter dollies built on or after March 1, 1998 must have which safety feature?
    显示答案

    答案: C. Antilock brakes, with a yellow lamp on the left

    Converter dollies built on or after March 1, 1998 must have antilock brakes and a yellow ABS lamp on the left side.

  12. 第12题，共25题

    Which trailer should go first, right behind the tractor?
    显示答案

    答案: C. The more heavily loaded one

    Put the heaviest trailer first, behind the tractor. The lighter trailer goes at the rear.

  13. 第13题，共25题

    Where should the lighter trailer go in a set of doubles?
    显示答案

    答案: B. At the rear

    The lighter trailer goes in the rear, and the heavier one goes first.

  14. 第14题，共25题

    The rear trailer has no spring brakes. How can you secure it before coupling?
    显示答案

    答案: B. Charge its tank, then disconnect the emergency line

    Charging the tank and disconnecting the emergency line sets the trailer's emergency brakes (if the slack adjusters are right). Chock the wheels if in doubt.

  15. 第15题，共25题

    You are not sure the rear trailer's brakes will hold. What should you do?
    显示答案

    答案: A. Chock the wheels

    If you have any doubt about the trailer brakes, chock the wheels.

  16. 第16题，共25题

    How do you release the brakes on a converter dolly that has no spring brakes?
    显示答案

    答案: A. Open the air tank petcock

    Open the dolly's air tank petcock to release its brakes. If the dolly has spring brakes, use the dolly parking brake control.

  17. 第17题，共25题

    The converter dolly is close to the rear trailer. How can you move it into place?
    显示答案

    答案: A. Wheel it by hand so it lines up with the kingpin

    If the distance is short, you can wheel the dolly by hand into line with the kingpin.

  18. 第18题，共25题

    After hooking the dolly to the first trailer, what must you do with the pintle hook?
    显示答案

    答案: D. Lock it

    Hook the dolly to the front trailer, lock the pintle hook, and secure the converter gear support in the raised position.

  19. 第19题，共25题

    Before backing the dolly under the rear trailer, how high should the trailer be?
    显示答案

    答案: D. Slightly lower than the dolly's fifth wheel

    The trailer must be a little low so it is raised slightly when the dolly is pushed under it.

  20. 第20题，共25题

    Why raise the rear trailer's landing gear slightly off the ground right after backing the dolly under it?
    显示答案

    答案: C. To prevent damage if the trailer moves

    Raise the landing gear just off the ground so it is not damaged if the trailer moves during the tug test.

  21. 第21题，共25题

    How do you test the coupling between the dolly and the second trailer?
    显示答案

    答案: C. Pull against the second trailer's kingpin

    Test the coupling by pulling gently against the second trailer's kingpin.

  22. 第22题，共25题

    During the visual check of the dolly coupling, what should you see?
    显示答案

    答案: A. No gap between the fifth wheel plates, jaws closed on the kingpin

    There should be no space between the fifth wheel surfaces, and the jaws must be closed on the kingpin.

  23. 第23题，共25题

    After coupling the dolly, what must you connect between the trailers?
    显示答案

    答案: D. Safety chains, air hoses and light cords

    Connect the safety chains, air hoses and light cords.

  24. 第24题，共25题

    After coupling doubles, what do you do with the shut-off valves at the rear of the second (last) trailer?
    显示答案

    答案: C. Close them

    Close the dolly air tank petcock and the shut-off valves at the rear of the last trailer.

  25. 第25题，共25题

    After coupling doubles, what do you do with the shut-off valves at the rear of the first trailer?
    显示答案

    答案: D. Open them

    Open the shut-off valves at the rear of the first trailer, and on the dolly if it has them, so air reaches the second trailer.

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 doubles/triples test has 20 questions in states such as Washington and Illinois, so you need 16 correct answers.
  • The double/triple trailers endorsement needs a knowledge test only.
  • The T endorsement cannot be placed on a commercial learner's permit.
  • Converter dollies built on or after March 1, 1998 must have antilock brakes, with a yellow lamp on the left side.

常见问题

How many questions are on the doubles and triples test?

Each state sets the number, but Washington and Illinois both use 20 questions. You need 16 correct to pass.

Is there a skills test for doubles and triples?

No. The T endorsement needs a knowledge test only.

Which trailer goes first in a set of doubles?

The more heavily loaded trailer goes first, right behind the tractor. The lighter trailer goes at the rear.

Which shut-off valves should be closed?

Only the ones at the rear of the last trailer. All others must be open so air reaches every trailer's brakes.

资料来源

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