Follow the railway (5)
I believe the answer is:
track
'follow' is the definition.
(I know that track is a more specific form of the action follow)
'the railway' is the wordplay.
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'railway' becomes 'rack' (rack railway is a kind of railway).
't'+'rack'='TRACK'
(Other definitions for track that I've seen before include "one of a number on record" , "Beaten path" , "Way" , "Foorprint or trail" , "Lines" .)