What’s operated by driver sitting (6)
I believe the answer is:
clutch
I believe this clue is a double definition.
'what's operated by driver' is the first definition.
(part of a car)
'sitting' is the second definition.
(sitting can mean a clutch of eggs sat on by a hen)
(Other definitions for clutch that I've seen before include "Hang on to" , "Hold the car mechanism tight" , "Depressing feature of car" , "Keep hold of" , "Seize - egg collection" .)