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Exams · Certifications · Licensing

CDL Combination Vehicles Test

Federal rules: practice questions

Our CDL Combination bank has 13 questions on this topic. Here are 4 of them with answers; the full mock exam draws from every topic, like the real one.

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Question 1

On a level, straight road, how far may a towed vehicle's path stray from the towing vehicle's path under federal rules?

  1. No more than 6 inches to either side
  2. No more than 3 inches to either side
  3. No more than 1 foot to either side
  4. No more than 1 inch to either side
Show the answer

B. No more than 3 inches to either side — 49 CFR 393.70(a): the towed vehicle's path must not deviate more than 3 inches to either side of the towing vehicle's path

Question 2

How many ways must an air-braked truck or tractor have to activate the trailer's emergency brakes?

  1. One automatic means only
  2. One manual control on the trailer
  3. Three, including a hand lever outside
  4. Two: one automatic and one manual control in the cab
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D. Two: one automatic and one manual control in the cab — 49 CFR 393.43(b): two means are required, one operating automatically on loss of air (20 to 45 psi) and one manual control operable from the driver's seat

Question 3

How many questions must you answer correctly to pass a 20-question combination test at the federal 80% standard?

  1. 16
  2. 14
  3. 15
  4. 18
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A. 16 — 80 percent of 20 is 16 (49 CFR 383.135(a)(1))

Question 4

Under federal rules, at what towing-vehicle air pressure must the tractor protection valve operate automatically?

  1. Between 20 and 45 psi
  2. Between 55 and 65 psi
  3. Between 80 and 85 psi
  4. Between 5 and 15 psi
Show the answer

A. Between 20 and 45 psi — 49 CFR 393.43(a): the tractor protection valve shall operate automatically when towing-vehicle air pressure is between 20 and 45 psi

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