This has actually been sitting in the back of my mind for a while. I've been cross-referencing sighting reports from the Midlands against old OS maps and there does seem to be a cluster of encounters within a half mile or so of disused railway corridors. Not just dogman type stuff either - big cat sightings, ufo flap zones, all sorts.
My working theory is that old rail lines often follow pre-existing routes, drovers roads, ancient trackways, that sort of thing. So you're potentially looking at corridors that have been significant landscape features for centuries before the Victorians ever laid a rail on them. If there's something to the earth mysteries angle - ley lines, geomagnetic variation along linear landscape features - then these routes might genuinely function as conduits for whatever this phenomenon actually is.
Has anyone done any proper mapping work on this? Would be really interested to compare notes with people who have local data from other regions. The US sighting databases are huge so theres probably enough data to test the correlation properly if someone wanted to dig into it.