I made a relation for the former right of way of the Maryland & Pennsylvania railroad. Check it out here: http://www.openstreetmap.org/browse/relation/3058279
Abandoned rail rights of way are one of OSM's strong suits. These old paths are often used for trails or roads in modern times, thus they are beneficial.
Making this relation was pretty easy because all the ways were already there. I just connected them. There are some spurs that I could still add, and as I was scanning along the route, I was suprised by how many populated areas are not mapped well. I'll add them as map notes!