The most common and most likely answer to this crossword clue is the 16 letter word PELICANÂ CROSSING
I've seen this crossword clue in The Guardian
P
E
L
I
C
A
N
Â
C
R
O
S
S
I
N
G
Buddy explains!

The straight part
We know that "One on the road" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one on the road = pelican crossing.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.