Road’s ruined: bumps initially accumulate on the surface (6)
I believe the answer is:
adsorb
'accumulate on the surface' is the definition.
(to adsorb is to hold molecules on a surface)
'road's ruined bumps initially' is the wordplay.
'ruined' indicates an anagram.
'initially' suggests taking the first letters.
The initial letter of 'bumps' is 'b'.
'roads' is an anagram of 'adsor'.
'adsor'+'b'='ADSORB'
(Other definitions for adsorb that I've seen before include "Hold film of gas or liquid molecules on surface" , "Accumulate film on the surface" .)