247SimpleTests
CDL · Inspection

During the pre-trip inspection of a doubles combination, what must be verified about the dolly's connection to the second semitrailer?

Correct answer

The dolly's fifth wheel must be properly coupled to the second trailer's kingpin (using the same verification as a primary fifth wheel coupling: tug test, jaw engagement, no high hookup); safety chains crossed; air lines connected; lights functioning

  1. A Only that the dolly is visible
  2. B The dolly's fifth wheel must be properly coupled to the second trailer's kingpin (using the same verification as a primary fifth wheel coupling: tug test, jaw engagement, no high hookup); safety chains crossed; air lines connected; lights functioning
  3. C Only verify the dolly's tires
  4. D The second connection requires no inspection

Why this is the answer

The dolly-to-second-trailer coupling is a full fifth wheel coupling that requires the identical inspection as the primary tractor-to-trailer coupling: back the dolly under the second trailer's kingpin at the correct height; confirm jaw engagement; perform the tug test with the dolly's brakes set; verify no high hookup; connect air lines and electrical; verify safety chains are crossed with correct slack. A failed dolly coupling at highway speed separates the rear half of the combination.
Source: FMCSA CDL Manual, Chapter 7, Doubles and Triples, Dolly-to-Trailer Coupling Inspection

Practice more questions

This question is from our CDL Practice Tests practice test. Take the full practice test to test your knowledge across all Inspection and other topics.

Take the Doubles and Triples practice test →

New to this exam? Our CDL exam guide explains the format, scoring, and how to prepare.

Related questions

Inspection

What additional inspection items are unique to doubles and triples?

 Inspection

How do you check the trailer brakes work on a doubles combination?

 Inspection

What is special about checking the air system on a doubles combination?

 Inspection

What endorsement is required to drive doubles and triples?

State-specific guides

Need information for your state? Our state guides cover local requirements, fees, and what to expect on exam day.

California Texas Florida New York Pennsylvania Illinois Ohio Georgia

Recommended study materials

Study guide

CDL Study Guide 2025–2026 (Trivium)

Complete prep for all CDL written tests: general knowledge, air brakes, combination vehicles, hazmat, and all endorsements. Includes full-length practice tests.

Check Price → Study guide

CDL Practice Tests & Flashcards (Accepted Inc.)

600+ practice questions covering every FMCSA knowledge area, plus 400 flashcards for endorsement prep.

Check Price → Study guide

Master the CDL Truck Driver's License (Arco)

Arco's classic CDL prep with in-depth FMCSA manual coverage, endorsement chapters, and scored practice exams.

Check Price →

As an Amazon Associate, CJ Affiliate, and AWIN publisher we earn from qualifying purchases. Links above are affiliate links. Full disclosure →