****UPDATE*****
WMATA reports, there will be no rail service between Rosslyn and Pentagon stations due to the ongoing investigation into the October 12th derailment between Rosslyn and Arlington Cemetery stations. Free shuttle buses will replace trains between Rosslyn, Arlington Cemetery, and Pentagon stations.
There has been a train derailment of a Metro car heading from the Arlington Cemetery area to Rosslyn. The Metro has shut down trains running on these specific rails. Expect delays along the Blue Line - suspension of service between Foggy Bottom and Pentagon. Seek another route and avoid the area.