Vessel that road carries north (5)
I believe the answer is:
aorta
'vessel' is the definition.
(blood vessel)
'that road carries north' is the wordplay.
'carries' says the answer is hidden in the clue.
'north' shows that the letters should be reversed in order (in a down clue, letters go up or 'north').
'atroa' is hidden within 'that road'.
'atroa' written backwards gives 'AORTA'.
(Other definitions for aorta that I've seen before include "Main artery from heart" , "A rota (anag)" , "Heart's great artery" , "Principal artery" , "Major blood vessel" .)