11 a.m. update:

There has been a bit of confusion as to whether riders on the disabled train had to evacuate into the tunnel. Some initial reports on Twitter seemed to suggest that people were going to have to climb into the tunnel, but a rider on that train and Metro both tell us that is not the case.

Here’s what Alison Gary, who was on the disabled train bound for Branch Avenue, told us:

Caroline Lukas, a spokeswoman for Metro, said that no riders climbed into the tunnel.

The disabled train, which halted at the Shaw station, snarled service on multiple lines this morning. Green and Yellow Line trains were severely delayed in both directions, with backups also stretching onto the Blue Line in Virginia. As a result, riders encountered crowded platforms and long waits at stations across the region.

— Mark Berman

Update, 9:43 a.m.:

Normal service has resumed on the Green and Yellow lines.

Update, 9:05 a.m.:

Metro reports that the disabled Green Line train has been offloaded and is on the move towards Greenbelt.

Trains are no longer single-tracking, but residual delays of 25 to 30 minutes will continue due to congestion at stations, according to Metro.

Update, 8:53 a.m.:

Delays on Green and Yellow lines appear to be getting worse. Metro said customers are now facing delays of 25 to 30 minutes, but some riders report that they’ve been waiting longer.

Original post, 8:20 a.m.:

Metro is reporting delays on the Green and Yellow lines due to a disabled train at the Shaw-Howard University station.

Trains on both lines are single-tracking between U Street and Mount Vernon Square. Metro said riders can expect delays of up to 20 minutes in both directions.

Metro advises that the Red Line is a good alternative between Fort Totten and Gallery Place.