At a distance, service area's backed up (4)
I believe the answer is:
afar
'at a distance' is the definition.
(I've seen this before)
'service area's backed up' is the wordplay.
'service' becomes 'raf'.
'area' becomes 'a' (maths abbreviation).
'backed up' shows that the letters should be reversed in order.
'raf'+'a'='rafa'
'rafa' back-to-front is 'AFAR'.
(Other definitions for afar that I've seen before include "Many miles away" , "A long way away" , "Way-out" , "Inhabitant of Ethiopia" , "A long distance away" .)