Car that's at home in the road (4)
I believe the answer is:
mini
'car' is the definition.
(Mini Cooper)
'at home in the road' is the wordplay.
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'in the' indicates putting letters inside.
'road' becomes 'mi' (**).
'in' going into 'mi' is 'MINI'.
'that's' acts as a link.
(Other definitions for mini that I've seen before include "Baby" , "Italian Job car?" , "Once fashionable skirt" , "Short skirt - small car" , "Iconic economy car (introduced in 1959)" .)