Railway lines are interesting because they follow really old routes, a lot of them built over drovers roads or even older tracks that go back centuries. So you're not necessarily looking at the railway itself as the cause, more like the railway followed something that was already there.
I've done a fair bit of fieldwork around disused lines in the Scottish Borders and the topography is always the same - embankments, cuttings, overgrown corridors. Perfect cover for something large to move without being seen. That's mundane, not paranormal, but it matters.
What I'd want to know from anyone reporting sightings is whether these are active or disused lines, and roughly what region. The pattern only means something if the data is consistent. Anyone actually keeping a proper log of this or is it just vibes and YouTube thumbnails at this point.