CDL Doubles and Triples Practice Test

All 33 questions with answers

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1. Which endorsement letter lets a Class A driver pull double and triple trailers?

   1. D
   2. T
   3. P
   4. N
   Show answer

   B. T T is for double/triple trailers. N is tank vehicle and P is passenger. (49 CFR 383.153)

2. What testing does the doubles/triples endorsement require?

   1. Both a knowledge and a skills test
   2. A skills test only
   3. A knowledge test only
   4. No test, only training
   Show answer

   C. A knowledge test only Federal rules require a knowledge test for the T endorsement. Passenger and school bus endorsements need a skills test as well. (49 CFR 383.93(c)(1))

3. Compared with other commercial vehicles, doubles and triples are:

   1. Less stable, with more things that can go wrong
   2. Less likely to jackknife
   3. Just as stable
   4. More stable because of the extra axles
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   A. Less stable, with more things that can go wrong More trailers mean more parts to fail and less stability, so they need extra care. (CDL manual: Doubles and Triples)

4. A speed that is safe on a curve for a single-trailer rig is:

   1. Required by law for all combinations
   2. Also safe for doubles and triples
   3. Possibly too fast for doubles and triples
   4. Too slow for doubles
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   C. Possibly too fast for doubles and triples Steer gently and go slowly around corners, ramps and curves. A curve speed that suits a straight truck or single trailer may roll a set of doubles or triples. (CDL manual: Doubles and Triples)

5. In a set of triples, which trailer is most likely to turn over?

   1. The first one
   2. The last one
   3. They are equally likely
   4. The middle one
   Show answer

   B. The last one The crack-the-whip effect grows toward the back of the train, so the last trailer is most likely to roll. (CDL manual: Doubles and Triples)

6. What causes the crack-the-whip effect?

   1. Rearward amplification of a quick steering move
   2. Low tire pressure
   3. Worn fifth wheels
   4. Air lines that are too short
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   A. Rearward amplification of a quick steering move A sudden steering move is amplified at each trailer back from the tractor. Quick lane changes can turn the rear trailer over. (CDL manual: Combination Vehicles (steer gently))

7. The manual gives triples a rearward amplification of:

   1. 2.0
   2. 3.5
   3. 5.0
   4. 1.5
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   B. 3.5 You can roll the last trailer of triples 3.5 times as easily as a five-axle tractor. (CDL manual: Combination Vehicles (steer gently))

8. A rearward amplification of 2.0 means:

   1. The rear trailer is twice as likely to turn over as the tractor
   2. The rig is twice as long as a tractor
   3. The rig needs twice the following distance
   4. The rear trailer brakes twice as hard
   Show answer

   A. The rear trailer is twice as likely to turn over as the tractor The number compares how likely the rear trailer is to roll with the tractor in a quick lane change. (CDL manual: Combination Vehicles (steer gently))

9. Why should you look far ahead when pulling doubles or triples?

   1. To save fuel
   2. So you can slow down or change lanes gradually
   3. To spot weigh stations early
   4. Because the mirrors do not work
   Show answer

   B. So you can slow down or change lanes gradually These rigs must be driven very smoothly to avoid a rollover or jackknife. Seeing trouble early lets you react gently. (CDL manual: Doubles and Triples)

10. You pull a 70-foot set of doubles at 50 mph. How much following distance should you leave?

    1. 8 seconds
    2. 7 seconds
    3. 12 seconds
    4. 4 seconds
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    A. 8 seconds At least 1 second for each 10 feet of length (7 seconds), plus 1 more over 40 mph: 8 seconds. (CDL manual: Combination Vehicles (steer gently))

11. Doubles and triples need more space than other commercial vehicles because they:

    1. Must stay in the right lane
    2. Are longer and cannot be turned or stopped suddenly
    3. Have more mirrors
    4. Accelerate faster
    Show answer

    B. Are longer and cannot be turned or stopped suddenly Allow more following distance, bigger gaps to enter or cross traffic, and check the sides are clear before changing lanes. (CDL manual: Doubles and Triples)

12. Why are doubles and triples more likely to skid in bad weather?

    1. Their tires are smaller
    2. They are longer and have more dead axles pulled by the drive axles
    3. Their trailers are lighter
    4. They cannot use chains
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    B. They are longer and have more dead axles pulled by the drive axles More length and more dead axles for the drive axles to pull mean more chance of skids and lost traction on slippery roads and mountains. (CDL manual: Doubles and Triples)

13. When parking doubles or triples, you should avoid:

    1. Parking on level ground
    2. A spot you cannot pull straight through
    3. Truck stops
    4. Using the parking brake
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    B. A spot you cannot pull straight through Know how the lot is laid out so you do not end up with a long, difficult way out. (CDL manual: Doubles and Triples)

14. Converter dollies built on or after what date must have antilock brakes?

    1. March 1, 1998
    2. July 1, 2010
    3. March 1, 2005
    4. January 1, 1990
    Show answer

    A. March 1, 1998 Air-braked vehicles other than truck tractors, including converter dollies, built on or after March 1, 1998 must have ABS. (49 CFR 393.55(c)(2))

15. How can you tell a converter dolly has antilock brakes?

    1. It has a sticker on the fifth wheel
    2. It has a blue glad hand
    3. It has a yellow lamp on the left side
    4. It has red reflectors on the tongue
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    C. It has a yellow lamp on the left side Dollies with ABS carry a yellow lamp on the left side of the dolly. (CDL manual: Doubles and Triples)

16. For the safest handling, where should the more heavily loaded trailer go?

    1. First, right behind the tractor
    2. At the rear
    3. In the middle of triples
    4. It does not matter
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    A. First, right behind the tractor The heavier semitrailer goes in first position behind the tractor; the lighter one goes at the rear. (CDL manual: Doubles and Triples)

17. What is a converter dolly?

    1. A cart for moving cargo
    2. A coupling device with one or two axles and a fifth wheel
    3. A jack for lifting a trailer
    4. An air tank for the rear trailer
    Show answer

    B. A coupling device with one or two axles and a fifth wheel It lets a second semitrailer be coupled to the back of a tractor-trailer, making a double bottom rig. (CDL manual: Doubles and Triples)

18. The second trailer has no spring brakes. How do you secure it before coupling?

    1. Connect the emergency line, charge the trailer air tank, then disconnect the line
    2. Open the air tank petcock
    3. Lower the landing gear only
    4. Leave the emergency line connected while you work
    Show answer

    A. Connect the emergency line, charge the trailer air tank, then disconnect the line Disconnecting the charged emergency line sets the trailer emergency brakes, if the slack adjusters are right. Chock the wheels if you have any doubt. (CDL manual: Doubles and Triples)

19. How do you release the brakes on a converter dolly that has no spring brakes?

    1. Open the dolly air tank petcock
    2. Push in the red knob
    3. Disconnect the light cord
    4. Pull the trolley valve
    Show answer

    A. Open the dolly air tank petcock Opening the petcock bleeds the air tank and releases the dolly brakes. A dolly with spring brakes has its own parking brake control. (CDL manual: Doubles and Triples)

20. Before backing the dolly under the rear trailer, the trailer height should be:

    1. As low as the landing gear allows
    2. Well above the fifth wheel
    3. Level with the top of the dolly tires
    4. Slightly lower than the center of the fifth wheel
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    D. Slightly lower than the center of the fifth wheel The trailer should be raised slightly as the dolly is pushed under it. Too high and the kingpin may not couple correctly. (CDL manual: Doubles and Triples)

21. Right after backing the dolly under the rear trailer, the landing gear should be:

    1. Left on the ground
    2. Removed
    3. Fully raised and the handle stowed
    4. Raised slightly off the ground
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    D. Raised slightly off the ground Lifting it slightly prevents damage if the trailer moves. You raise it completely later, after the lines are connected. (CDL manual: Doubles and Triples)

22. When you check the coupling visually, you should see:

    1. The release arm pulled out
    2. A small gap between the upper and lower fifth wheel
    3. The kingpin resting on top of the jaws
    4. No space between the upper and lower fifth wheel, and the locking jaws closed on the kingpin
    Show answer

    D. No space between the upper and lower fifth wheel, and the locking jaws closed on the kingpin Any gap between the fifth wheel plates means the kingpin may not be locked. The jaws must close around the shank of the kingpin. (CDL manual: Doubles and Triples)

23. The shut-off valves at the rear of the LAST trailer should be:

    1. Removed
    2. Open
    3. Open on the service line only
    4. Closed
    Show answer

    D. Closed Closed at the very back so air does not escape. Valves at the rear of the trailers in front are open so air reaches every trailer. (CDL manual: Doubles and Triples)

24. In a set of triples, the shut-off valves at the rear of the MIDDLE trailer should be:

    1. Closed on the emergency line only
    2. Closed
    3. Open on the service line only
    4. Open
    Show answer

    D. Open Only the last trailer has its shut-offs closed. Every trailer in front of it must pass air back. (CDL manual: Doubles and Triples)

25. During inspection, the converter dolly air tank drain valve should be:

    1. Half open
    2. Removed
    3. Open
    4. Closed
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    D. Closed An open drain valve would let the dolly’s air escape. Also check the pintle eye is in the hook, the hook is latched and the safety chains are secured. (CDL manual: Doubles and Triples)

26. After coupling twins and charging the brakes, you open the emergency line shut-off at the rear of the second trailer and no air comes out. This means:

    1. The dolly has spring brakes
    2. The system is working normally
    3. You should drive to build pressure
    4. Something is wrong and the brakes will not work
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    D. Something is wrong and the brakes will not work Air must reach the back of the rig for all the brakes to work. Check that the shut-offs on the trailers and dollies are open. (CDL manual: Doubles and Triples)

27. Why must you never unlock the pintle hook while the dolly is still under the rear trailer?

    1. The air lines will cross
    2. The fifth wheel will lock
    3. The trailer brakes will release
    4. The dolly tow bar may fly up, possibly causing injury
    Show answer

    D. The dolly tow bar may fly up, possibly causing injury Pull the dolly out from under the rear trailer first. A tow bar that flies up can hurt someone and makes re-coupling very hard. (CDL manual: Doubles and Triples)

28. The first step in uncoupling the rear trailer of a set of twins is:

    1. Disconnect the air lines
    2. Pull the tractor forward
    3. Release the dolly brakes
    4. Park in a straight line on firm, level ground
    Show answer

    D. Park in a straight line on firm, level ground Then set the parking brakes, chock the second trailer if it has no spring brakes, and lower its landing gear to take some weight off the dolly. (CDL manual: Doubles and Triples)

29. Uncoupling the rear trailer, you lower its landing gear:

    1. All the way until the trailer lifts off the dolly
    2. Not at all
    3. Only after pulling the dolly out
    4. Enough to take some weight off the dolly
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    D. Enough to take some weight off the dolly Lowering it enough to remove some weight from the dolly makes it easier to release the dolly and pull it out. (CDL manual: Doubles and Triples)

30. To uncouple a triple-trailer rig, you start with:

    1. The middle dolly
    2. The first trailer
    3. The third trailer, by pulling its dolly out and then unhitching the dolly
    4. The tractor
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    C. The third trailer, by pulling its dolly out and then unhitching the dolly Take off the third trailer the same way as the rear trailer of doubles, then uncouple the rest as a double-bottom rig. (CDL manual: Doubles and Triples)

31. To check that air reaches all trailers, you open the emergency line shut-off at the rear of the last trailer. You should:

    1. See the spring brakes apply
    2. Hear air escaping, showing the whole system is charged
    3. Hear nothing
    4. See the red knob pop out
    Show answer

    B. Hear air escaping, showing the whole system is charged Then close it and do the same with the service line while the trailer hand brake or pedal is applied. No air means a shut-off valve is closed somewhere. (CDL manual: Doubles and Triples)

32. When you test the tractor protection valve by fanning off air, the trailer air supply knob should pop out, usually within:

    1. 60 to 80 psi
    2. 20 to 45 psi
    3. 5 to 10 psi
    4. 100 to 120 psi
    Show answer

    B. 20 to 45 psi In the range set by the manufacturer, usually 20 to 45 psi. If the valve fails, a trailer leak could drain the tractor’s air too. (CDL manual: Doubles and Triples)

33. You test the trailer service brakes with the hand valve. In normal driving, the trailer brakes should be controlled with:

    1. The parking brake
    2. The foot brake pedal
    3. The red trailer air supply knob
    4. The hand valve
    Show answer

    B. The foot brake pedal The hand valve (trolley valve) is for the test. In normal driving the foot pedal applies air to the service brakes at all wheels. (CDL manual: Doubles and Triples)