The most common and most likely answer to this crossword clue is the 5 plus 5 letter word BLACK MARIA
B
L
A
C
K
M
A
R
I
A
More clues leading to the result BLACK MARIA
- Nick vehicle from girl behind bar
- Where cops may sit for a game of cards
- Indication of disapproval mostly shown by one next to a police van
- Card game in vehicle going to Dartmoor?
- Miserable girl in police van
- Police van in a film studio
- Claim Akbar constructed a police car
- First American film studio's police van
Buddy explains!

The straight part
We know that "police car" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case police car = black maria.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.