There's a railroad on Long Island which has been abandoned for over a hundred years. The right-of-way is still very visible, however. Somebody (am too lazy to look up whom) decided that the right-of-way (ROW) should be preserved, so they didn't allow any development on the ROW. So, a bunch of backyards in Queens between 87th and 88th streets have extra-deep backyards, as do those between Stewart Road and Peck Avenue. Also, the Kissena Corridor (amenity=park) owes its existance to the protection of this ROW. A portion of the railroad at the very southern end was still being used until a couple of decades ago, so there's still an abandoned bridge (for which I need to get a photo for my Flickr page of such). But other than that, I know of no physical traces of the railroad.

They gave up protecting the ROW about 30 years ago, so there's a school built on it, plus a few apartment buildings. Tear those down, though, and you could run the railroad straight through everything.

http://www.openstreetmap.org/browse/way/24127063