The most common and most likely answer to this crossword clue is the 8 plus 7 letter word MOTORWAY MADNESS
I've seen this crossword clue in The Guardian
M
O
T
O
R
W
A
Y
M
A
D
N
E
S
S
Buddy explains!
The straight part
We know that "erratic driving" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case erratic driving = motorway madness.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.