Smash arises when ignoring area limit for road (4)
I believe the answer is:
kerb
'road' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for kerb that I've seen before include "Pavement edging" , "stone by the way" , "Roadway edge" , "Edge of road" , "Pavement's edge" .)