Transport protest (4)
I believe the answer is:
rail
I believe this is a double definition.
'transport' is the first definition.
(I know that rail is a more specific form of the action the transport)
'protest' is the second definition.
(I've seen this before)
(Other definitions for rail that I've seen before include "Protest strongly (at)" , "The Iron Horse road" , "Means of transport" , "Complain strongly or part of fence" , "Form of transport" .)