The laws vary from place to place, but as a practical matter, and certainly in more developed areas, railroad rights of way are part of the fabric of the area. Property lines and property uses are built around the former right of way, and it has a much higher value to society as a trail than it would divvying it up amongst adjoining property owners. I would hope to the extent possible, courts would fall on the side of the interests of the general public than individual property owners, who have a dubious claim at best.