Not my usual area but this has caught my attention lately. Been looking at the reports coming in through a few different databases and yeah, there does seem to be a pattern along old disused lines, particularly in rural areas where the tracks cut through woodland.
My theory, for what its worth, is its less about the lines themselves and more about what they created - long corridors through dense forest that wildlife uses as natural pathways. Whatever dogman is, if it exists, it would use the same routes everything else does.
Anyone actually had a sighting near one? I'd want to know the specific line, time of year, that sort of detail before I got too excited about the correlation. Correlations are easy to find if you go looking for them.