Police control hard to understand in areas to the west (5,4)
I believe the answer is:
speed trap
'police control' is the definition.
(I've seen this before)
'hard to understand in areas to the west' is the wordplay.
'hard to understand' becomes 'deep' (I've seen this before).
'in' indicates putting letters inside.
'areas' becomes 'parts' (I've seen this before).
'to the west' shows that the letters should be reversed in order (letters written right to left or \'east to west\').
'deep' placed within 'parts' is 'partdeeps'.
'partdeeps' backwards is 'SPEED TRAP'.
(Other definitions for speed trap that I've seen before include "road safety measure" , "hazard for travellers in haste?" , "Police control" , "something drivers might avoid" , "Set-up to catch fast drivers" .)