It's not really that new, and it's a stretch to call it a rail trail, but the West Campus Access Road along the edge of the Department of Homeland Security's headquarters at St. Elizabeths is now open and, despite some concern that it would not, includes a "10 foot multi-purpose trail' on one side.
View looking down toward Potomac
The road follows an old rail spur from the Shepherd Branch line that was used to deliver coal to the furnaces of Saint Elizabeths Hospital Complex. At some point St. Elizabeths stopped using coal and the spur was abandoned.
Google Maps labels this road as Firth Sterling Avenue, but all the documentation on it calls it the West Campus Access Road, I should have taken a photo of some street signs I suppose.
The trail with a grove of trees on one side and rain gardens on the other
The trail is nice, even if it's kind of just a wide sidewalk. There are few driveways and the whole way it runs along side rain gardens and tree groves. There are also nice views of the city (which my photos do not do justice to). You can see Alexandria, the Air Force Memorial, Washington Monument, Southwest Waterfront, Baseball Stadium, Capitol, both rivers and more.
Trust me, you can the Washington Monument in this photo
On the other side you get a pretty great view of the historic cemetery.
Historic Cemetery on the hillside
The trail doesn't, at this time, have any utility for someone not going to DHS, but it's a worth a trip at least once for the views. Because it used to be a rail line, it's a gentle climb up the escarpment. From a utility standpoint, it's frustrating because the end of the trail is only about 600 feet from Newcomb Street, SE. A connection to that would make this a nice way to bypass the worst part of South Capitol Street (until the South Capitol Street Trail is built) as well as providing other cycling and walking opportunities. But that will have to wait for Phase 2 when the Access Road will be extended to Malcolm X at Interstate 295, and hopefully the trail will be too.
The end of the trail (for now)
Trail beside the bus stops, with the woods through which the road and trail will extend beyond.
Like I said, this isn't really new. It opened as part of Phase 1 which was completed in 2013. Phase 2 will continue the access road as seen in the image below at bottom.
*I don't do this very often, but I'm going to toot my own horn here a bit since I may be partly responsible for this. Way back when the 2005 DC Bicycle master plan was being worked on, I suggested to Jim Sebastian that they use this old rail spur for a bike trail and Jim said they had been looking for a way to access the grounds, picked up a sharpie and drew it on the map [Whereas usually he just says to me "That's an interesting idea" and doesn't write anything down and then pretends to need to make a phone call]. It wound up being included in the official bike plan. When the St. Elizabeth's Master Plan was initially being worked on, it didn't include a trail, but by 2008 it did (though it wasn't a done deal), and as I recall the bike plan was part of the reason they included it (though, I think they saw the value in it too). I guess if I keep throwing enough crazy ideas out there, eventually one of them will catch on.