Yes actually, this is something I've been looking into for a while now. There's a real cluster of reports along old Victorian-era rail lines here in the south of England too, not just the American cases. My theory is its about the corridors themselves - old rail routes often follow natural ley lines or at least pre-existing wildlife paths that go back centuries, and whatever these things are they seem to use the same routes generation after generation.
The embankments are interesting as well. They create sheltered channels, good cover, and often run through land that hasn't been properly developed since the railways closed down. Lots of old tunnels and culverts too which people don't tend to go near.
Has anyone mapped the sightings against old Ordnance Survey rail maps? I started doing this with UK reports last year and the overlap is genuinely striking. Would love to compare notes with anyone else who's been tracking this pattern.