The most common and most likely answer to this crossword clue is the 9 letter word CYCLEPATH
I've seen this crossword clue in Financial Times
C
Y
C
L
E
P
A
T
H
Buddy explains!
The straight part
We know that "route forbidden to drivers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case route forbidden to drivers = cyclepath.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 CYCLEPATH mean?
CYCLEPATH noun- A path, segregated from other traffic, for the use of riders of bicycles