Persist in using withdrawn basic measure in motorway feature? (8)
I believe the answer is:
continue
'persist in' is the definition.
('continue' can be a synonym of 'persist in')
'withdrawn basic measure in motorway feature?' is the wordplay.
'withdrawn' says the letters should be written backwards.
'basic measure' becomes 'unit'.
'in' is an insertion indicator.
'motorway feature?' becomes 'cone' (as in a road cone).
'unit' back-to-front is 'tinu'.
'tinu' inserted within 'cone' is 'CONTINUE'.
'using' acts as a link.
(Other definitions for continue that I've seen before include "Proceed" , "Resume" , "Don't stop, keep going" , "Persist" , "Go on without stopping" .)