Free Doubles and Triples (T) CDL practice questions

Sample questions from this test

1. Compared with other commercial vehicles, doubles and triples are:
   1. More stable
   2. Less stable
   3. Equally stable
   4. More stable only when empty
   Show answer

   Less stable

   Doubles and triples are less stable, and more things can go wrong.

2. In a set of triples, which trailer is most likely to turn over in a quick lane change?
   1. The first trailer
   2. The middle trailer
   3. All are equally likely
   4. The last trailer
   Show answer

   The last trailer

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

3. Why should you look far ahead when pulling doubles or triples?
   1. So you can slow down or change lanes gradually
   2. To read the DOT number
   3. To keep the ABS lamp off
   4. So you can drive faster
   Show answer

   So you can slow down or change lanes gradually

   They must be driven very smoothly; looking far ahead lets you make gradual changes.

4. Why are doubles and triples more likely to skid in bad weather and mountain driving?
   1. Their brakes are weaker
   2. They cannot use tire chains
   3. They have more length and more dead axles to pull with the drive axles
   4. They cannot use the foot brake
   Show answer

   They have more length and more dead axles to pull with the drive axles

   Greater length and more dead axles mean more chance of skids and loss of traction.

5. How can you tell a converter dolly has antilock brakes?
   1. It has red glad hands
   2. It has a yellow lamp on the left side
   3. It has a blue lamp on the right side
   4. It has two axles
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   It has a yellow lamp on the left side

   These dollies have a yellow ABS lamp on the left side.

6. For the safest handling, where should the more heavily loaded trailer be?
   1. In first position, right behind the tractor
   2. In the rear position
   3. In the middle of a triple only
   4. It does not matter
   Show answer

   In first position, right behind the tractor

   Put the heavier trailer first behind the tractor and the lighter one in the rear.

7. How do you release the brakes on a converter dolly without spring brakes?
   1. Push in the air supply knob
   2. Pull the trolley valve
   3. Open the air tank petcock
   4. Close the shut-off valves
   Show answer

   Open the air tank petcock

   Release dolly brakes by opening the air tank petcock (or use the dolly parking brake control if it has spring brakes).

8. What do you check when making a visual check of the dolly coupling?
   1. That the ABS lamp is lit
   2. No space between upper and lower fifth wheel and the locking jaws closed on the kingpin
   3. That the landing gear is on the ground
   4. That the glad hands are crossed
   Show answer

   No space between upper and lower fifth wheel and the locking jaws closed on the kingpin

   Look for no gap between the upper and lower fifth wheel, and for jaws closed on the kingpin.

9. What three things connect the dolly and trailers besides the coupling itself?
   1. Landing gear, crank and chocks
   2. ABS lamp, ECU and sensors
   3. Mud flaps, reflectors and tires
   4. Safety chains, air hoses and light cords
   Show answer

   Safety chains, air hoses and light cords

   Connect safety chains, air hoses and light cords.

10. Why should you pull the dolly out from under the rear trailer before disconnecting it from the trailer in front?
    1. If you unlock the pintle hook with the dolly under the trailer, the tow bar may fly up
    2. The dolly brakes will lock
    3. The ABS will turn off
    4. The rear trailer will roll away
    Show answer

    If you unlock the pintle hook with the dolly under the trailer, the tow bar may fly up

    Unlocking the pintle hook while the dolly is still under the rear trailer can make the tow bar spring up and hurt you.

11. When uncoupling a triple-trailer rig, which trailer do you uncouple first?
    1. The first trailer
    2. The second trailer
    3. The third trailer
    4. Any order is fine
    Show answer

    The third trailer

    Uncouple the third trailer first by pulling the dolly out, then unhitching the dolly.

12. In a set of doubles, the shut-off valves at the rear of the FIRST trailer should be:
    1. Closed
    2. Open
    3. Half open
    4. Removed
    Show answer

    Open

    Rear of front trailers: OPEN. Rear of last trailer: CLOSED.

13. What should you check on the pintle hook during inspection?
    1. That it is greased like a fifth wheel
    2. That it is open
    3. That the ABS lamp is near it
    4. That the dolly pintle eye is in place and the hook is latched
    Show answer

    That the dolly pintle eye is in place and the hook is latched

    Be sure the pintle eye of the dolly is in the pintle hook and the pintle hook is latched.

14. When inspecting doubles, what should you check about the light cords?
    1. That they are coiled on the dolly
    2. That they are unplugged to save power
    3. That they are firmly in their sockets on the trailers
    4. That they are crossed with the air lines
    Show answer

    That they are firmly in their sockets on the trailers

    Be sure light cords are firmly in the sockets on the trailers.

15. During the air flow test, why must the trailer hand brake or brake pedal be applied when you open the service line valve?
    1. To set the ABS
    2. To keep the landing gear up
    3. So there is air in the service line to come out
    4. To close the tractor protection valve
    Show answer

    So there is air in the service line to come out

    The service line only has air when the brakes are applied, so the test assumes the hand brake or pedal is on.