CDL Doubles and Triples Sample Questions

Questions from each area of the CDL Doubles and Triples test. Pick an answer to see whether you're right, how everyone else did, and why.

CDL Doubles and Triples Test exam guide

1 Procedures for assembly and hookup of the units

You are about to release the pintle hook to unhitch the converter dolly. First you should:

  1. lower the dolly landing gear and release its spring brakes.
  2. raise the dolly landing gear and release its spring brakes.
  3. lower the dolly landing gear and set its spring brakes.

Answer: C, lower the dolly landing gear and set its spring brakes.. The dolly must stand on its own and stay still before you free it. So you lower its landing gear, unhook the safety chains, and set its spring brakes or chock it. Then you release the pintle hook and pull clear slowly (CDL manual 7.2.2).

During your walk-around, you see a light cord only partly pushed into its trailer socket. What should you do?

  1. Leave it if the trailer lights still come on.
  2. Write it up on your report at the end of the day.
  3. Push it firmly into the socket before you drive.

Answer: C, Push it firmly into the socket before you drive.. Light cords must sit firmly in the trailer sockets. A loose plug can shake out on the road, and the trailer lights would go dark. Fix it before you drive. (CDL manual 7.3.1)

2 Proper placement of heaviest trailer

In a set of doubles with one heavy and one light trailer, the heavy trailer goes:

  1. next to the tractor, in front.
  2. in either spot; it makes no difference.
  3. last, at the tail of the set.

Answer: A, next to the tractor, in front.. Couple the heavier trailer first, right behind the tractor, and put the lighter one last. This order keeps the rig steadier and easier to control. (CDL manual 7.2.1)

Your heavier trailer, set to ride first, has its load packed along one wall. What should you do?

  1. Leave it, because a heavy front trailer stays stable.
  2. Swap it to the rear, behind the lighter trailer.
  3. Reload it so the weight is centered and spread across the floor.

Answer: C, Reload it so the weight is centered and spread across the floor.. A load on one side makes the trailer lean, and a leaning trailer rolls over more easily. Center the load and spread it out, and keep the heavier trailer first. (CDL manual 6.1.1, 7.2.1)

3 Handling and stability characteristics

You are moving from a single-trailer rig to pulling doubles. Compared with your old rig, doubles are:

  1. more stable, since the load is spread out.
  2. less stable, with more parts that can fail.
  3. equally stable, since each trailer is shorter.

Answer: B, less stable, with more parts that can fail.. Pulling two or three trailers adds joints, axles and parts that can fail. These rigs sway and tip more easily than single-trailer rigs, so they need extra care. (CDL manual 7.1)

A chart gives a set of doubles a rearward amplification of 2.0. What does that mean?

  1. The rig takes twice as long to stop as the tractor alone.
  2. The last trailer tips over twice as easily as the tractor.
  3. The last trailer off-tracks twice as far as the tractor.

Answer: B, The last trailer tips over twice as easily as the tractor.. Rearward amplification shows how much a sudden steering move grows toward the back of the rig. At 2.0, the last trailer is two times as likely as the tractor to overturn. (CDL manual 6.1.2)

4 Potential problems in traffic operations

You are pulling doubles in heavy traffic. Why do you need more space around you?

  1. They are longer and can't stop or turn quickly.
  2. They are wider and carry more weight on each axle.
  3. Both of the above.

Answer: A, They are longer and can't stop or turn quickly.. Doubles are longer than other rigs, and you can't stop or turn them suddenly. So leave more following distance and bigger gaps in traffic. (CDL manual 7.1.5)

A car is tailgating your doubles rig on a two-lane road. You should:

  1. speed up to put more space between you and the car.
  2. leave more room ahead and slow down only gradually.
  3. tap your brakes so your brake lights warn the driver.

Answer: B, leave more room ahead and slow down only gradually.. More room in front means you won't have to stop or swerve suddenly, and the car gets a chance to go around. A crash is less harmful at a slow speed (CDL manual 2.7.2).

5 Operating practices and procedures not otherwise specified

Before you drive a set of doubles into a parking lot you don't know, you should:

  1. learn how its lanes and spaces are laid out.
  2. take the first open space near the entrance.
  3. plan to back the rig out when you leave.

Answer: A, learn how its lanes and spaces are laid out.. A set of doubles needs a lot of room to leave. Learn the lot's layout before you go in, so you don't end up with a long, hard way out. (CDL manual 7.1.7)

Another name for the trailer air supply control is the:

  1. trailer hand valve.
  2. trailer service valve.
  3. trailer emergency valve.

Answer: C, trailer emergency valve.. This red knob has more than one name. You may hear it called the trailer emergency valve. It also works the tractor protection valve. (CDL manual 6.5.2, 7.4.1)