The most common and most likely answer to this crossword clue is the 9 letter word COMMUTERS
I've seen this crossword clue in The Guardian
C
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M
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More clues leading to the result COMMUTERS
Buddy explains!

The straight part
We know that "regular travellers /regular travellers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case regular travellers /regular travellers = commuters.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 COMMUTERS mean?
COMMUTERS noun- One who commutes (etymology 1).
- A person who regularly travels from one place to another, typically to work.
- A piece of transportation equipment used for the transportation of such persons.