Run into train track (5)
I believe the answer is:
trail
This clue is a triple definition!
'run' is the first definition.
(thesaurus)
'into' is a link.
'train' is the second definition.
(thesaurus)
'track' is the third definition.
(I know that trail is a type of track)
(Other definitions for trail that I've seen before include "Drop behind" , "Drag along the ground" , "Wake" , "Track or mark left by something that has passed" , "Need to catch up with" .)