Selfish driver (7)
'selfish driver' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for road hog that I've seen before include "Mr Toad, for one" , "Selfish and dangerous driver" , "Driver who obstructs others" , "Reckless motorist" , "Inconsiderate motorist" .)
(Another definition for roadhog that I've seen is " Reckless driver".)