Metro officials restricted Green Line service Friday afternoon after smoke was reported in a tunnel in Southwest Washington.
The incident happened underground between the L’Enfant Plaza and Waterfront stations about 5:45 p.m., said Morgan Dye, a Metro spokeswoman.
The smoke was believed to have come from an arcing insulation, the part on the track that keeps electricity from the third rail away from other parts.
Officials estimated delays of about 15 minutes as they restricted service to a single track in that area.
No injuries were immediately reported.