A "set of doubles" typically refers to:
Correct. A "set of doubles" is one tractor pulling two trailers (typically two pups, each about 28 feet long, in LTL operations).
CDL Practice Question #363
Category: Doubles/Triples
Why this question matters
This question is one of 50 in our Doubles/Triples bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.