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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.

  • المركبات التجارية
  • الولايات المتحدة
  • عدد الأسئلة: 50
  • تمت المراجعة في 10 أكتوبر 2026

إجابة سريعة

عدد أسئلة الاختبار الرسمي: 20. درجة النجاح: Varies by state; usually 20 questions, with 16 correct needed (80%). الجهة المنظِّمة: Your state driver licensing agency, under federal rules set by FMCSA (49 CFR Part 383). تدرّب هنا مجانًا على 50 من الأسئلة، مع الإجابة والشرح لكل سؤال. تمت مراجعته مقارنةً بالمصادر الرسمية في 10 أكتوبر 2026.

اقرأ قبل أن تتدرّبابدأ بقراءة «CDL Doubles and Triples Study Guide»: ملاحظات بلغة بسيطة ورسوم توضيحية والأرقام التي يجب تذكّرها.

  1. السؤال 1 من 25

    Compared with other combinations, how likely are doubles and triples to turn over?
    أظهر الإجابة

    الإجابة: D. More likely

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

  2. السؤال 2 من 25

    Which trailer in a double or triple is most likely to turn over?
    أظهر الإجابة

    الإجابة: D. The last trailer

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

  3. السؤال 3 من 25

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

    الإجابة: 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. السؤال 4 من 25

    A speed that is safe for a single trailer on a curve is not always safe for doubles. Why?
    أظهر الإجابة

    الإجابة: 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. السؤال 5 من 25

    What is the crack-the-whip effect?
    أظهر الإجابة

    الإجابة: 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. السؤال 6 من 25

    Why do doubles and triples need extra care in the pre-trip inspection?
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    أظهر الإجابة

    الإجابة: C. They have more critical parts to check

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

  7. السؤال 7 من 25

    Why should you look far ahead when pulling doubles or triples?
    أظهر الإجابة

    الإجابة: 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. السؤال 8 من 25

    How should your following distance compare when pulling doubles or triples?
    أظهر الإجابة

    الإجابة: A. Allow more following distance

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

  9. السؤال 9 من 25

    Why are doubles and triples more likely to skid in bad weather?
    أظهر الإجابة

    الإجابة: 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. السؤال 10 من 25

    What should you avoid when parking doubles or triples?
    أظهر الإجابة

    الإجابة: 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. السؤال 11 من 25

    Converter dollies built on or after March 1, 1998 must have which safety feature?
    أظهر الإجابة

    الإجابة: 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. السؤال 12 من 25

    Which trailer should go first, right behind the tractor?
    أظهر الإجابة

    الإجابة: C. The more heavily loaded one

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

  13. السؤال 13 من 25

    Where should the lighter trailer go in a set of doubles?
    أظهر الإجابة

    الإجابة: B. At the rear

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

  14. السؤال 14 من 25

    The rear trailer has no spring brakes. How can you secure it before coupling?
    أظهر الإجابة

    الإجابة: 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. السؤال 15 من 25

    You are not sure the rear trailer's brakes will hold. What should you do?
    أظهر الإجابة

    الإجابة: A. Chock the wheels

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

  16. السؤال 16 من 25

    How do you release the brakes on a converter dolly that has no spring brakes?
    أظهر الإجابة

    الإجابة: 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. السؤال 17 من 25

    The converter dolly is close to the rear trailer. How can you move it into place?
    أظهر الإجابة

    الإجابة: 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. السؤال 18 من 25

    After hooking the dolly to the first trailer, what must you do with the pintle hook?
    أظهر الإجابة

    الإجابة: 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. السؤال 19 من 25

    Before backing the dolly under the rear trailer, how high should the trailer be?
    أظهر الإجابة

    الإجابة: 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. السؤال 20 من 25

    Why raise the rear trailer's landing gear slightly off the ground right after backing the dolly under it?
    أظهر الإجابة

    الإجابة: 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. السؤال 21 من 25

    How do you test the coupling between the dolly and the second trailer?
    أظهر الإجابة

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

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

  22. السؤال 22 من 25

    During the visual check of the dolly coupling, what should you see?
    أظهر الإجابة

    الإجابة: 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. السؤال 23 من 25

    After coupling the dolly, what must you connect between the trailers?
    أظهر الإجابة

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

    Connect the safety chains, air hoses and light cords.

  24. السؤال 24 من 25

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

    الإجابة: C. Close them

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

  25. السؤال 25 من 25

    After coupling doubles, what do you do with the shut-off valves at the rear of the first trailer?
    أظهر الإجابة

    الإجابة: 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.

ما يجب معرفته قبل الاختبار

  • 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.

الأسئلة الشائعة

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.

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