Follow rail (5)
I believe the answer is:
track
I believe this clue is a double definition.
'follow' is the first definition.
(I know that track is a more specific form of the action follow)
'rail' is the second definition.
(I know that rail can be written as track)
(Other definitions for track that I've seen before include "one of a number on record" , "Rough path or road" , "Path; rails; circuit" , "Trace; path" , "Sign that one's passed" .)