The most common and most likely answer to this crossword clue is the 7 letter word SLEIGHS
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More clues leading to the result SLEIGHS
Buddy explains!

The straight part
We know that "winter transport" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case winter transport = sleighs.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SLEIGHS mean?
SLEIGHS noun- A vehicle, generally pulled by an animal, which moves over snow or ice on runners, used for transporting persons or goods. (contrast "sled", which is smaller)
- To ride or drive a sleigh.