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Combination Vehicles Practice Question 27

Required for Class ACombination Vehicles · Question 27

A converter dolly is used to:

• ACool brakes
• BConnect a second trailer behind a first to form a double
• CLift the trailer
• DReplace the fifth wheel

Correct answer: B. Connect a second trailer behind a first to form a double

Why: A converter dolly is a small wheeled frame with a fifth wheel that converts a semi-trailer into a full trailer for use behind another trailer in a double or triple combination.

How this question fits the Combination test

Articulated vehicles fail in unique ways: trailer swing under braking, rearward amplification under steering, and jackknife under loss of traction. Combination Vehicle knowledge is required for any Class A applicant under 49 CFR 383.111.

Study technique for this topic

Walk through the coupling sequence verbally until it's second nature. Know the safe-rolling rearward amplification factor, the difference between trailer service brakes and parking brakes, and what creates the conditions for a tractor jackknife.

Related Combination practice questions

• Q26. The legal maximum trailer length on the National Network is generally:
• Q40. When approaching an intersection in a combination vehicle, you should:
• Q53. The blind spots of a tractor-trailer include:
• Q2. The 'fifth wheel' on a tractor is:
• Q15. To prevent rollover with a high center of gravity, you should:

Continue your CDL preparation

The Combination Vehicles portion of the CDL knowledge exam covers more than this single question. Use this site's full Combination Vehicles bank to drill every topic, then test yourself with one of our state-specific practice sets to confirm you are ready for the actual DMV exam in your state. Always check your state's CDL handbook for any local addenda before the test day.

If you are still building your overall CDL foundation, start with the General Knowledge bank — every CDL applicant must pass it — and then work outward to the endorsements you plan to add.