Main road is a pain (4)
I believe the answer is:
drag
I believe this is a double definition.
'main road' is the first definition.
(informal term for a road)
'pain' is the second definition.
(thesaurus)
'is a' is the link.
(Other definitions for drag that I've seen before include "Haul - queen's garb?" , "Resistance to motion" , "Women's clothes worn by a man - pull" , "Become tedious" , "Haul - a bore!" .)