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CDL · General

When coupling doubles, what is a converter dolly?

Correct answer

A coupling device with a fifth wheel that connects the rear trailer to the front trailer — it has its own axle(s) and is used to convert a semi-trailer into a full trailer that can be pulled behind another trailer

  1. A A tool for changing tires
  2. B A coupling device with a fifth wheel that connects the rear trailer to the front trailer — it has its own axle(s) and is used to convert a semi-trailer into a full trailer that can be pulled behind another trailer
  3. C A type of engine
  4. D A trailer brake

Why this is the answer

CONVERTER DOLLY: A coupling device used to connect a second (or third) trailer in a doubles or triples combination. COMPONENTS: A frame with one or more axles; a fifth wheel mounted on top (to receive the kingpin of the rear trailer); a tow bar/drawbar with an eye that connects to the pintle hook of the trailer ahead; its own brakes and lights; FUNCTION: It 'converts' a semi-trailer (which needs a fifth wheel for support) into a full trailer that can be towed behind the first trailer; COUPLING WITH A DOLLY involves: connecting the dolly to the rear of the first trailer (pintle hook and safety chains), then backing the rear trailer onto the dolly's fifth wheel (like coupling a tractor to a trailer); the dolly creates an additional coupling point that must be inspected and secured carefully; DOUBLES/TRIPLES have multiple coupling points (tractor-to-trailer, dolly connections) — each must be properly secured; the converter dolly is central to doubles/triples operation and is a key inspection and coupling topic on the endorsement exam.
Source: FMCSA CDL Manual — Doubles/Triples, Converter Dolly

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Related questions

General

When coupling a converter dolly to the rear trailer, what safety device must be connected in addition to the pintle hook?

 General

Before backing the second trailer onto the converter dolly's fifth wheel, what should the driver check about the dolly?

 General

After coupling a complete set of doubles, what is a key final check before driving?

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