This 7-mile line, built in 1917, stretched from Accotink Station on the Richmond, Fredericksburg and Potomac Railroad (CSX today) in Newington to Fort Belvior, a post about 10 miles south of Alexandria. The line was used to serve coal for heating at both the post itself as well as a nearby government prison, along with other miscellaneous freight.
Railroad operations along the line ceased in 1993. The line from the CSX connection to a local road is still largely intact but overgrown. The trackage along the remainder of the line has been removed.
Thanks to Tim Moriarty for contributing information about this route.