Lengthy pedestrian crossing built up (5)
I believe the answer is:
hyped
'built up' is the definition.
(to hype something is to build it up)
'lengthy pedestrian crossing' is the wordplay.
'crossing' indicates the answer is hidden within the clue (the clue crosses over the answer).
'HYPED' is hidden in the letters of 'lengthy pedestrian'.
(Other definitions for hyped that I've seen before include "Intensively promoted" , "Given exaggerated publicity" .)