Parking away from bypass, go downhill (3)
I believe the answer is:
ski
'go downhill' is the definition.
(go down a hill on skis)
'parking away from bypass' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'away from' suggests deleting specific letters.
'bypass' becomes 'skip' (I've seen this in another clue).
'skip' with 'p' taken out is 'SKI'.
(Other definitions for ski that I've seen before include "Hit the slopes" , "Snow-runner" , "go uphill? Probably not!" , "What one might do in Alps" , "Winter sport equipment" .)