Protest about method of travel (4)
I believe the answer is:
rail
I believe this is a double definition.
'protest' is the first definition.
(I've seen this before)
'method of travel' is the second definition.
'about' is the link.
(Other definitions for rail that I've seen before include "Abuse, scold" , "Horizontal bar - bird - complain" , "Bar of track or fence" , "Bar; waterside bird" , "Complain strongly or part of fence" .)