The most common and most likely answer to this crossword clue is the 7 plus 5 letter word TRAFFIC LIGHT
I've seen this crossword clue in The Daily Telegraph
T
R
A
F
F
I
C
L
I
G
H
T
Buddy explains!
The straight part
We know that "Few vehicles about/this will control them" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case few vehicles about/this will control them = traffic light.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.