CDL Doubles and Triples Practice Test

Pick an answer for each question. You’ll see right away if it’s correct and why.

1. 1. When pulling doubles, where should the heavier semitrailer go?

   A. First, right behind the tractor B. Last, at the rear C. It doesn't matter if both are under the weight limit D. On the converter dolly
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   Answer: A. First, right behind the tractor Put the heavier trailer first, behind the tractor, and the lighter one in the rear. A heavy rear trailer makes the rig less stable.

2. 2. In a combination with two or three trailers, which one is most likely to turn over?

   A. The first trailer B. The last trailer C. The tractor D. They are all equally likely
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   Answer: B. The last trailer The last trailer is the most likely to roll because a quick steering move gets amplified toward the back of the rig.

3. 3. With triples, the last trailer is about how many times easier to roll over than the tractor in a five-axle rig?

   A. The same B. 1.5 times C. 3.5 times D. 10 times
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   Answer: C. 3.5 times The manual gives triples a rearward amplification of 3.5. That's the crack-the-whip effect, so steer gently and avoid sudden lane changes.

4. 4. What is a converter dolly?

   A. A valve that converts service air to emergency air B. The sliding fifth wheel on the tractor C. A spare axle carried under the trailer D. A towed unit with its own axle(s) and a fifth wheel that connects the second trailer to the one ahead
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   Answer: D. A towed unit with its own axle(s) and a fifth wheel that connects the second trailer to the one ahead The dolly hooks to the first trailer's pintle hook and gives the next semitrailer a fifth wheel to couple to, turning the rig into doubles or triples.

5. 5. During the walk-around, how should the air shut-off valves be set?

   A. Open at the rear of the front trailers, closed at the rear of the last trailer B. Closed on every trailer C. Open on every trailer, including the last D. Closed on the front trailers, open on the last
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   Answer: A. Open at the rear of the front trailers, closed at the rear of the last trailer Air has to flow back through every trailer, so the front trailers' valves stay open. The last trailer's valves stay closed so the air doesn't escape.

6. 6. How do you confirm that air is reaching all the trailers?

   A. Watch the tractor's air gauge only B. At the rear of the last trailer, open the emergency line valve and listen for air, then close it C. Kick the tires on each trailer D. Check that the glad hands are warm
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   Answer: B. At the rear of the last trailer, open the emergency line valve and listen for air, then close it With the system charged, open the emergency line valve at the very back; escaping air shows it's charged. Do the same for the service line with the brakes applied, then close both.

7. 7. A converter dolly built on or after March 1, 1998 must have antilock brakes. How can you tell?

   A. A red lamp on the right side B. A sticker on the tow bar C. A yellow lamp on the left side of the dolly D. A blue glad hand
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   Answer: C. A yellow lamp on the left side of the dolly Dollies built on or after March 1, 1998 need ABS, shown by a yellow malfunction lamp on the left side of the dolly.

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

   A. It sets the dolly brakes B. The air lines will leak C. The lights will short out D. The tow bar can fly up and injure you
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   Answer: D. The tow bar can fly up and injure you With the trailer's weight on the dolly, the tow bar can spring up when released. Lower the trailer's landing gear and pull the dolly out first.

9. 9. The second trailer has no spring brakes. How do you hold it in place before coupling?

   A. Connect the emergency line, charge the trailer tank, then disconnect it to set the emergency brakes B. Leave the trailer air lines connected to the dolly C. Set the trailer hand valve D. Lower the landing gear all the way to the ground and drive on
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   Answer: A. Connect the emergency line, charge the trailer tank, then disconnect it to set the emergency brakes Charging the trailer tank and then disconnecting the emergency line sets its emergency brakes, if the slack adjusters are right. Chock the wheels if you're not sure the brakes will hold.

10. 10. How high should the second trailer be when you back the dolly under it?

    A. Well above the dolly's fifth wheel B. Slightly lower than the center of the fifth wheel, so it rises as the dolly goes under C. Resting on its nose D. Any height, because the dolly adjusts
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    Answer: B. Slightly lower than the center of the fifth wheel, so it rises as the dolly goes under Same idea as a tractor coupling: the trailer should sit slightly low so it gets lifted as the dolly backs under, then you check that the jaws closed on the kingpin.

11. 11. When uncoupling the rear trailer, what do you do before pulling the dolly out?

    A. Unlock the pintle hook B. Remove the safety chains from the first trailer C. Lower the rear trailer's landing gear to take weight off the dolly D. Open the dolly air tank drain and drive off
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    Answer: C. Lower the rear trailer's landing gear to take weight off the dolly Lower the landing gear to take the weight off the dolly, close the air shut-offs, disconnect the dolly lines, release the dolly brakes and the fifth wheel latch, then pull slowly forward.

12. 12. How should your following distance with doubles or triples compare to other commercial vehicles?

    A. The same B. Shorter, since doubles brake better C. It only matters at night D. Longer
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    Answer: D. Longer The manual says to allow more following distance with doubles and triples, and to make sure gaps are big enough before you enter or cross traffic.

13. 13. What's the safest way to steer a doubles or triples rig?

    A. Gently, avoiding quick lane changes B. Quickly, so the trailers follow faster C. With small jerks to keep the trailers in line D. Only with the trailer hand valve applied
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    Answer: A. Gently, avoiding quick lane changes Sudden steering causes the crack-the-whip effect that can tip the rear trailer. Smooth, early steering and slow turns keep the rig stable.

14. 14. In a turn, which part of a doubles or triples rig off-tracks the most?

    A. The tractor's steer axle B. The last trailer C. The first trailer D. The converter dolly tongue
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    Answer: B. The last trailer The longer the rig, the more it off-tracks, and the last trailer cuts inside the most. Plan wide enough turns to keep it clear of curbs and objects.

15. 15. When inspecting the dolly connection, what should you confirm?

    A. The dolly air tank drain valve is open B. The safety chains are removed so the dolly can turn C. The pintle eye is in the pintle hook, the hook is latched and the safety chains are secured D. Any spare tire on the dolly is loose for quick access
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    Answer: C. The pintle eye is in the pintle hook, the hook is latched and the safety chains are secured Check that the pintle eye sits in a latched pintle hook and the safety chains are attached. Also keep the dolly air tank drain closed and any spare tire secured.

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