The most common and most likely answer to this crossword clue is the 4 plus 4 letter word DIRT BIKE
I've seen this crossword clue in The Guardian
D
I
R
T
B
I
K
E
More clues leading to the result DIRT BIKE
Buddy explains!

The straight part
We know that "vehicle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vehicle = dirt bike.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.