This is something I've been tracking for quite a few years now and the correlation is genuinely striking. In the West Midlands alone I've catalogued at least fourteen accounts since the late 1990s where witnesses placed the encounter within roughly half a mile of disused or active rail corridors. The Sutton Park line gets mentioned repeatedly.
My working theory is that the railway embankments and cuttings create a kind of sheltered movement corridor - thick vegetation, minimal human foot traffic, and the embankments themselves often run through older woodland that predates the railway by centuries. If you're a large cryptid moving between territories, that's an attractive route.
What I'd want to know from anyone posting here is whether the sightings cluster near active lines, disused lines, or both. Because the acoustic profile is very different and I suspect if this animal uses low-frequency sound for communication or navigation, the vibration signature of an active line might actually be relevant.
Has anyone mapped their local sightings against historical OS maps showing old rail routes? Would be worth doing properly.