A man who called himself King John was on the Red Line on his way to the Medical Center Metro stop—headed to Briana's Hair Spa in Frederick, where he's a master barber. He was in the third car. It just stopped. "It was a slight bang," he said. "It wasn't major."
There was uncertainty, the flickering [...]

Metro has reported the derailment of a six-car Red Line train at the Farragut North station.
Metro's statement in full:
A six-car Red Line train headed in the direction of Shady Grove Metrorail station has reportedly derailed near the Farragut North Metrorail station. There are no reported injuries.
Metro officials and local first responders are at the scene [...]

At this moment, Dr. Gridlock is in the vanguard of Washington Post coverage of this afternoon's train mishap in Northeast D.C. The item credits WJLA-TV and CNN for key facts on the accident.
Here's one commenter from the washingtonpost.com on the matter:
How is the Washington Post being scooped about a potentially serious metro rail collision? This [...]

Comes this dispatch, via Dr. Gridlock:
A Red Line Metrorail train derailed at 5:10 p.m. approaching Fort Totten in the Shady Grove-bound side. Trains are turning back at Brookland and Takoma....Metro says that shuttle bus service has been requested to bridge the gap between Takoma and Brookland.

There are reports of injuries. Developing.
UPDATE, 5:35 P.M.: This seems [...]