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CDL Test: Doubles and triples questions and answers

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Doubles and triples

34 questions

  1. #1

    Which trailer in a doubles or triples combination is most likely to turn over?

    1. The first trailer
    2. The middle trailer
    3. The last trailer
    4. They are all equally likely

    Answer: C. The last trailer is the most likely to turn over (crack-the-whip effect).

    Source: Pennsylvania CDL Manual (PUB 223), 7.1.2 Beware of the Crack-the-whip Effectthe last trailer in a combination is most likely to turn over.

  2. #2

    When pulling doubles, where should the more heavily loaded trailer be?

    1. First, right behind the tractor
    2. Last, at the rear
    3. It does not matter
    4. On the converter dolly

    Answer: A. Put the more heavily loaded semitrailer first behind the tractor; the lighter trailer goes at the rear.

    Source: Pennsylvania CDL Manual (PUB 223), 7.2.1 Coupling Twin Trailersthe more heavily loaded semitrailer should be in first position behind the tractor.

  3. #3

    How do you release the brakes on a converter dolly before moving it into position?

    1. Push in the trailer air supply knob
    2. Pull the trailer hand valve
    3. Disconnect the safety chains
    4. Open the dolly air tank petcock

    Answer: D. Release dolly brakes by opening the air tank petcock (if the dolly has spring brakes, use the dolly parking brake control).

    Source: Pennsylvania CDL Manual (PUB 223), 7.2.1 Coupling Twin Trailersrelease dolly brakes by opening the air tank petcock.

  4. #4

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

    1. The trailer brakes will release
    2. The dolly tow bar may fly up and cause injury
    3. The air lines will freeze
    4. The landing gear will drop

    Answer: B. The tow bar may fly up, possibly causing injury and making it very hard to re-couple.

    Source: Pennsylvania CDL Manual (PUB 223), 7.2.2 Uncoupling Twin Trailersnever unlock the pintle hook with the dolly still under the rear trailer.

  5. #5

    On doubles and triples, the shut-off valves at the rear of the FRONT trailers should be:

    1. Open
    2. Closed
    3. Removed
    4. Taped shut

    Answer: A. Rear of front trailers: OPEN; rear of last trailer: CLOSED; dolly air tank drain valve: CLOSED.

    Source: Pennsylvania CDL Manual (PUB 223), 7.3.1 Additional Checksrear of front trailers: OPEN.

  6. #6

    To check that air flows to all trailers, after charging the system you open the emergency line shut-off valve at:

    1. The front of the first trailer
    2. The converter dolly
    3. The rear of the last trailer
    4. The tractor protection valve

    Answer: C. Open the emergency line shut-off at the rear of the last trailer; you should hear air escaping, showing the whole system is charged.

    Source: Pennsylvania CDL Manual (PUB 223), 7.4.1 Additional Air Brake Checksopen the emergency line shut-off valve at the rear of the last trailer.

  7. #7

    Where is the ABS malfunction lamp on a converter dolly built on or after March 1, 1998?

    1. On the dashboard only
    2. On the right rear corner
    3. On the tow bar
    4. On the left side of the dolly

    Answer: D. Converter dollies built on or after March 1, 1998 must have ABS and a yellow lamp on the left side of the dolly.

    Source: Pennsylvania CDL Manual (PUB 223), 7.1.8 Antilock Braking Systems on Converter Dolliesthese dollies will have a yellow lamp on the left side of the dolly.

  8. #8

    A curve speed that is safe for a single-trailer rig is, for doubles or triples:

    1. Possibly too fast
    2. Always safe
    3. Too slow
    4. Safe if loaded evenly

    Answer: A. A safe curve speed for a straight truck or single-trailer rig may be too fast for doubles or triples.

    Source: Pennsylvania CDL Manual (PUB 223), 7.1.1 Prevent Trailer from Rolling OverA safe speed on a curve for a straight truck or a single trailer combination vehicle may be too fast for a set of doubles or triples.

  9. #9

    During the walkaround inspection of doubles or triples, the shut-off valves at the rear of the last trailer should be:

    1. Open
    2. Closed
    3. Open on the service line and closed on the emergency line
    4. Removed for the trip

    Answer: B. The rear of the last trailer must be closed; the rear of the front trailers must be open.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 99Rear of last trailer: CLOSED.

  10. #10

    The converter dolly air tank drain valve should be checked to be:

    1. Open
    2. Half open
    3. Open only in cold weather
    4. Closed

    Answer: D. The drain valve (petcock) on the dolly air tank must be closed before driving.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 99Converter dolly air tank drain valve: CLOSED.

  11. #11

    To secure a second trailer that has no spring brakes before coupling, you should connect the emergency line, charge the trailer air tank, and then:

    1. Disconnect the emergency line
    2. Leave the emergency line connected
    3. Open the trailer air tank drain
    4. Release the tractor parking brake

    Answer: A. Disconnecting the emergency line after charging sets the trailer emergency brakes.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97If the second trailer doesn’t have spring brakes, drive the tractor close to the trailer, connect the emergency line, charge the trailer air tank, and disconnect the emergency line. This will set the trailer emergency brakes (if the slack adjusters are correctly adjusted).

  12. #12

    When securing the second trailer, what should you do if you have any doubt about its brakes?

    1. Lower the landing gear fully
    2. Open the emergency line shut-off
    3. Chock the wheels
    4. Drive the trailer to a shop first

    Answer: C. Chocks give a sure hold if the brakes may not be reliable.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97Chock the wheels if you have any doubt about the brakes.

  13. #13

    After backing the converter dolly under the rear trailer, how do you test the coupling?

    1. Roll the dolly back and forth by hand
    2. Release the trailer brakes and push
    3. Pull against the pin of the second semitrailer
    4. Raise the landing gear fully and check

    Answer: C. A pull test shows whether the pin is really locked in the fifth wheel.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 98Test coupling by pulling against pin of the second semitrailer.

  14. #14

    A visual check of the coupling of the second semitrailer should show:

    1. No space between the upper and lower fifth wheel and the locking jaws closed on the kingpin
    2. A small gap between the upper and lower fifth wheel so the trailer can pivot freely
    3. The locking jaws open and resting on top of the kingpin head, with the trailer unlocked
    4. The kingpin sitting visibly above the top of the fifth wheel plate with no jaws visible

    Answer: A. A properly coupled fifth wheel has no gap and jaws closed on the kingpin.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 98Make visual check of coupling. (No space between upper and lower fifth wheel. Locking jaws closed on kingpin.)

  15. #15

    Before backing a converter dolly under the rear trailer, the trailer height must be:

    1. Slightly higher than the center of the fifth wheel
    2. Exactly level with the top of the dolly tires
    3. Lowered until the trailer rests on its landing gear pads
    4. Slightly lower than the center of the fifth wheel

    Answer: D. The trailer should be raised slightly as the dolly is pushed under it.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 98Make sure trailer height is correct. (It must be slightly lower than the center of the fifth wheel, so trailer is raised slightly when dolly is pushed under.)

  16. #16

    When inspecting the lower fifth wheel, the locking jaws should be around:

    1. The head of the kingpin, not the shank
    2. The shank of the kingpin, not the head
    3. The glide plate of the trailer
    4. The release arm of the fifth wheel

    Answer: B. Jaws around the head instead of the shank mean the coupling is not safe.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 99Locking jaws around the shank, not the head of kingpin.

  17. #17

    With a sliding fifth wheel, you must check that it is not so far forward that:

    1. The air and electrical lines will stretch so far that the trailer brakes get no air
    2. The tractor frame will hit the landing gear or the cab hit the trailer during turns
    3. The kingpin cannot lock into the jaws and the trailer will drop onto the tractor frame
    4. The dolly cannot be released and the landing gear cannot be raised fully

    Answer: B. A fifth wheel too far forward can cause the tractor to strike the trailer in turns.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 99Check that fifth wheel is not so far forward that tractor frame will hit landing gear, or cab hit the trailer, during turns.

  18. #18

    When checking that air flows to all trailers, you wait for air pressure to reach normal and then:

    1. Pull out the red trailer air supply knob
    2. Open the drain on each air tank
    3. Release the tractor parking brake
    4. Push in the red trailer air supply knob

    Answer: D. The trailer air supply knob supplies air to the emergency (supply) lines when pushed in.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100Wait for air pressure to reach normal, then push in the red “trailer air supply” knob.

  19. #19

    During the air flow check, you do not hear air escaping from both lines at the rear. What should you check?

    1. That the shut-off valves on the trailers and dollies are open
    2. That the tires on all trailers are inflated to full pressure
    3. That the landing gear on each trailer is fully raised and locked
    4. That the safety chains are crossed under the dolly drawbar

    Answer: A. Air must reach the back for all the brakes to work, so closed valves are the first thing to check.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100If you do NOT hear air escaping from both lines, check that the shut-off valves on the trailer(s) and dolly(ies) are in the OPEN position.

  20. #20

    When testing the tractor protection valve, the trailer air supply control should pop out when pressure falls usually within the range of:

    1. 5 to 15 psi
    2. 50 to 80 psi
    3. 20 to 45 psi
    4. 90 to 120 psi

    Answer: C. It should pop out within the manufacturer's range, usually 20 to 45 psi.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100The trailer air supply control (also called the tractor protection valve control) should pop out (or go from “normal” to “emergency” position) when the air pressure falls into the pressure range specified by the manufacturer. (Usually within the range of 20 to 45 psi.)

  21. #21

    If the tractor protection valve does not work properly, what could happen?

    1. The trailer brakes would never apply, even with the pedal fully pressed
    2. The engine would shut off automatically to protect the compressor
    3. A hose or trailer brake leak could drain all the air from the tractor
    4. The fifth wheel jaws would unlock and the trailer would roll free

    Answer: C. Losing the tractor's air can bring on the emergency brakes with possible loss of control.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100If the tractor protection valve doesn’t work properly, an air hose or trailer brake leak could drain all the air from the tractor.

  22. #22

    To test the trailer emergency brakes, after placing the trailer air supply control in the emergency position you should:

    1. Pull gently on the trailer with the tractor
    2. Back up hard against the trailer
    3. Apply the trailer hand valve and drive forward fast
    4. Shut the engine off and step on the brake pedal

    Answer: A. A gentle pull shows whether the trailer emergency brakes are holding.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100Pull gently on the trailer with the tractor to check that the trailer emergency brakes are on.

  23. #23

    Trailer brakes should be tested with the hand valve, but in normal operation they should be controlled with:

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

    Answer: D. The foot pedal applies air to the service brakes at all wheels.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100The trailer brakes should be tested with the hand valve, but controlled in normal operation with the foot pedal, which applies air to the service brakes at all wheels.

  24. #24

    When uncoupling a triple-trailer rig, the first step is to uncouple the third trailer by:

    1. Unhitching the dolly first, then pulling it out from under the trailer
    2. Pulling the dolly out, then unhitching it as when uncoupling doubles
    3. Disconnecting the tractor from the first trailer, then lowering the landing gear
    4. Lowering the first trailer's landing gear, then pulling the tractor ahead

    Answer: B. The third trailer is uncoupled first; the rest is uncoupled like any double-bottom rig.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 99Uncouple third trailer by pulling the dolly out, then unhitching the dolly using the method for uncoupling doubles.

  25. #25

    How many steps are in the inspection procedure used to inspect a double or triple combination vehicle?

    1. Three
    2. Seven
    3. Five
    4. Ten

    Answer: B. The same seven-step procedure from Section 2 is used, with extra checks.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 99Use the seven-step inspection procedure described in Section 2 to inspect your combination vehicle.

  26. #26

    Compared with other commercial vehicles, doubles and triples need you to:

    1. Allow less following distance
    2. Follow at the same distance as a single trailer
    3. Rely on quick turns to avoid hazards
    4. Allow more following distance

    Answer: D. They are longer and cannot be turned or stopped suddenly, so they need more space.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97Allow more following distance.

  27. #27

    Why is there more chance of skids and loss of traction when driving doubles or triples in bad weather?

    1. You have greater length and more dead axles to pull with your drive axles
    2. The trailers weigh much less than a single trailer, so the tires lose grip
    3. The tractor has only one drive axle when it pulls two or three trailers
    4. The brakes on doubles and triples are always out of adjustment in bad weather

    Answer: A. More dead axles must be pulled by the same drive axles, so traction is easier to lose.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97You will have greater length and more dead axles to pull with your drive axles than other drivers.

  28. #28

    When parking doubles or triples, you should make sure you do not get into a spot:

    1. With a level surface
    2. That has a lot of room
    3. You cannot pull straight through
    4. Near the exit of the lot

    Answer: C. Learn how lots are laid out to avoid a long, difficult escape.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97Make sure you do not get in a spot you cannot pull straight through.

  29. #29

    When uncoupling the rear trailer of a set of doubles, you should park the rig:

    1. On a slight downhill slope
    2. At an angle to ease the pull
    3. In a straight line on firm level ground
    4. On soft ground to cushion the trailer

    Answer: C. A straight, firm, level spot makes uncoupling safe and keeps the trailers aligned.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 98Park rig in a straight line on firm level ground.

  30. #30

    When uncoupling the rear trailer, the landing gear of the second semitrailer is lowered enough to:

    1. Remove some weight from the dolly
    2. Lift the trailer completely off the ground
    3. Release the fifth wheel latch
    4. Charge the trailer air tank

    Answer: A. Lowering the landing gear takes weight off the dolly before it is pulled out.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 98Lower landing gear of second semitrailer enough to remove some weight from dolly.

  31. #31

    After releasing the converter dolly fifth wheel latch, how do you get the dolly out from under the rear semitrailer?

    1. Back the tractor and first semitrailer up quickly
    2. Unlock the pintle hook first and drive away
    3. Raise the rear trailer with the tractor brakes
    4. Slowly pull the tractor, first semitrailer, and dolly forward

    Answer: D. The dolly is pulled out with the front of the rig still attached to it.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 98Slowly pull tractor, first semitrailer, and dolly forward to pull dolly out from under rear semitrailer.

  32. #32

    In the tractor protection valve test, with the engine off, how do you reduce the air pressure in the tanks?

    1. Open the drain valves of all tanks
    2. Step on and off the brake pedal several times
    3. Pull out the parking brake valve
    4. Disconnect the service air line

    Answer: B. Pumping the pedal lowers the pressure until the trailer air supply control pops out.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 100Step on and off the brake pedal several times to reduce the air pressure in the tanks.

  33. #33

    Doubles and triples must be driven very smoothly in order to avoid:

    1. Excess tire wear only
    2. Rollover or jackknife
    3. Fuel leaks
    4. Brake fade only

    Answer: B. Smooth driving, looking far ahead, helps you slow down or change lanes gradually.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97Doubles and triples must be driven very smoothly to avoid rollover or jackknife.

  34. #34

    A converter gear (dolly) is a coupling device of one or two axles and a fifth wheel that is used to:

    1. Lock the tractor's drive axles together so they turn at the same speed on slippery roads
    2. Store spare tires and tire chains under the trailer so they are ready for bad weather
    3. Raise the front of a trailer off the ground when its landing gear fails, so it can be towed
    4. Couple a semitrailer to the rear of a tractor-trailer combination, forming a double bottom rig

    Answer: D. The dolly lets a second semitrailer be pulled behind the first.

    Source: North Dakota CDL Manual (AAMVA model), Section 7, p. 97A converter gear on a dolly is a coupling device of one or two axles and a fifth wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig.
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