Italian town’s main road crossing smaller thoroughfare? (4)
I believe the answer is:
asti
'italian town's' is the definition.
'main road crossing smaller thoroughfare?' is the wordplay.
'main road' becomes 'ai' (resembles As, major UK road).
'crossing' indicates putting letters inside.
'smaller thoroughfare?' becomes 'st' (this could be a standard abbreviation of which I'm unaware).
'ai' going around 'st' is 'ASTI'.
(Other definitions for asti that I've seen before include "Sparkling wine named after an Italian Piedmont town" , "Sparkling white wine" , "Italian wine - (then change a letter for ...)" , "18" , "Piedmont wine city, SE of Turin" .)