Updated at 3:53 p.m.:

Metro trains are no longer single-tracking, but delays continue in both directions.

Original story:

Commuters at the Smithsonian Metro station reported seeing smoke and hearing a boom that Metro officials say was likely a brush between the third rail and its protective cover.

“What we believe happened is that a cover board came in contact with the third rail” at about 2:42 p.m., said Metro spokesman Dan Stessel. “That would result in an explosion and maybe a spark.” The train coming through the station at the time of the explosion has been inspected, he said, and there was no fire and no injuries.

There are, however, delays. Orange and Blue Line trains are now single-tracking between Smithsonian and Federal Center SW stations, and riders can expect delays in both directions, according to Metro.