Main road is a nuisance (4)
I believe the answer is:
I believe this clue is a double definition.
'main road' is the first definition.
(informal term for a road)
'nuisance' is the second definition.
'is a' is the link.
(Other definitions for drag that I've seen before include "Bind" , "Transvestite's garb" , "Trail; bore" , "Resistance to motion" , "Trail along the ground" .)