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CDL combination vehicles (Class A) practice test

30 free practice questions for this exam, each with the reason for the answer and where to look it up.

CDL general knowledge, air brakes, combination: practice test

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

Practice tests that prepare you for this exam

CDL general knowledge, air brakes, combination

The knowledge tests every commercial driver takes: general knowledge, air brakes, combination vehicles and the pre-trip inspection.

30 questions for this exam

About the exam

ExamCDL combination vehicles (Class A)
Who runs itState DMVs
WhereUnited States

Question count, time limit and pass mark differ by where you take it. Check the official candidate bulletin from the organisation that runs your exam.

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
Show the answer

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
Show the answer

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
Show the answer

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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