The most common and most likely answer to this crossword clue is the 9 letter word COACHLOAD
I've seen this crossword clue in The Times
C
O
A
C
H
L
O
A
D
More clues leading to the result COACHLOAD
Buddy explains!

The straight part
We know that "A lot of passengers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a lot of passengers = coachload.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 COACHLOAD mean?
COACHLOAD noun- As much or as many as can fill a coach.