Transport? Parking suggests a long walk (5)
I believe the answer is:
tramp
'a long walk' is the definition.
(I've seen this before)
'transport? parking' is the wordplay.
'transport?' becomes 'tram' (tram is a kind of transport).
'parking' becomes 'p'.
'tram'+'p'='TRAMP'
'suggests' acts as a link.
(Other definitions for tramp that I've seen before include "March heavily like hobo" , "I usually walk" , "man down on his luck" , "Tread heavily (on)" , "Disreputable wanderer" .)