Investigators are focusing on a failed section of 24-year-old rail as the possible cause of the first major incident on the Metro rail system of 2018.
Sixty-three riders were evacuated when a Red Line train derailed just after leaving the Farrugut North Station at about 6:30 a.m. Monday.
Metro officials warned that single-tracking disruption on the Red Line may continue into Tuesday.
There were no injuries. The evacuation took about two hours to complete. Riders were escorted by emergency workers as they walked about 200 yards to the Metro Center Station.
"It was a really large bump. It felt like the train had run over something really solid," said rider Martha Le.
Rider Gavin Bowman described the sounds of crunching metal and grinding concrete.
The incident occurred nearly three years to the day that a rider was killed by smoke when a train caught fire near the L'Enfant Plaza Station in 2015. The incident exposed radios that did not work underground and a bungled attempt to ventilate the tunnel with fresh air during the emergency.
This time Fire/EMS rescuers radios worked flawlessly and ventilation was set up immediately, according to Metro officials.
Federal investigators were on the scene of Monday's derailment.
The section of track where the incident occurred is considered to be among the most robust areas of the system. It is not in an area where Safe-Track improvements have been made or are planned.
The suspect section of rail was installed in 1993 and passed an inspection in August. Rail typically has a 50-year lifetime.