The old right of way for the B&O (later CSX) Mt. Airy Loop (later branch). This was the end of the branch for many years after half the loop was pulled up in 1975. However the last major business these tracks served moved up to Perryville, MD and so the tracks were pulled up after 2007.

http://www.trainweb.org/oldmainline/omlloop1.htm
http://www.gazette.net/stories/0831.....20_32363.shtml

Rail traffic is up by large margins over the past few decades, but more traffic has consolidated to main lines.