Does sensible thing as driver and stops talking (5,2)
I believe the answer is:
belts up
I believe this clue is a double definition.
'does sensible thing as driver' is the first definition.
(belt up can mean to put on a seatbelt)
'stops talking' is the second definition.
'and' acts as a link.
(Other definitions for belts up that I've seen before include "Keeps quiet" , "like a sensible motorist does" , "Buttons it" , "observes safety procedure before journey" .)