The most common and most likely answer to this crossword clue is the 12 letter word STRAPHANGERS
I've seen this crossword clue in The Times
S
T
R
A
P
H
A
N
G
E
R
S
Buddy explains!
The straight part
We know that "Travellers gripping" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case travellers gripping = straphangers.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 STRAPHANGERS mean?
STRAPHANGERS noun- A person who travels using public transportation (often standing up and holding on to a strap).