Traffic stopper? (5,4)
I believe the answer is:
speed trap
'traffic stopper?' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for speed trap that I've seen before include "Hazard for fast motorist" , "something drivers might avoid" , "hazard for travellers in haste?" , "inconvenience for boy racers?" , "Where you may see police" .)