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Combination practice questions

30 questions from the cdl general knowledge, air brakes, combination practice test.

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Combination practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Compared with an empty rig, how much more likely is a fully loaded rig to roll over in a crash?

  1. 2 times
  2. 5 times
  3. 10 times
  4. 50 times
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C. 10 times

A fully loaded rig is about ten times more likely to roll over in a crash than an empty one, because the load raises the center of gravity. That is why cargo is kept low and turns are taken slowly.

Reference: CDL Manual Section 6.1, Driving Combination Vehicles Safely

What is rearward amplification?

  1. The crack-the-whip effect that can tip the rear trailer
  2. The extra braking force the rear trailer axles produce
  3. The way a trailer cuts inside the tractor in a turn
  4. The delay before air reaches the brakes of the rear trailer
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A. The crack-the-whip effect that can tip the rear trailer

A quick lane change is magnified toward the back of a combination, so the last trailer can roll over even when the tractor stays upright. A trailer cutting inside the tractor's path in a turn is offtracking.

Reference: CDL Manual Section 6.1, Driving Combination Vehicles Safely

How does a bobtail tractor (no trailer) stop compared with a loaded tractor-semitrailer?

  1. It can take longer to stop
  2. It always stops much shorter
  3. It stops in the same distance
  4. It cannot lock its wheels
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A. It can take longer to stop

With no trailer weight on the drive axles a bobtail has poor traction, its wheels lock easily, and tests show it can take longer to stop than a loaded combination. Being lighter does not make it stop shorter.

Reference: CDL Manual Section 6.1, Driving Combination Vehicles Safely

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