Quiet road transport (5)
I believe the answer is:
plane
'transport' is the definition.
(plane is a kind of transport)
'quiet road' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'road' becomes 'lane' (a lane is a small road).
'p'+'lane'='PLANE'
(Other definitions for plane that I've seen before include "Nepal (anag.)" , "Form of transport" , "Aircraft - level surface - carpenter's tool" , "Woodworker's tool" , "Woodworking tool" .)