By Brittny Mejia

The Washington Metropolitan Area Transit Authority says train service in the nation's capital is operating on a modified schedule on some lines the day after an incident at a Metro station killed one person and hospitalized dozens more.

Eighty-four patients were taken to hospitals and more than 200 people were evaluated after smoke filled a subway tunnel and L'Enfant Plaza Metro station. As of Tuesday morning, MedStar Washington Hospital center said it had six patients _ one in critical condition, one in serious and four in good condition. The status of patients sent to other hospitals wasn't clear.

The National Transportation Safety Board is investigating the incident, which started about 3 p.m. EST. It was caused by an electrical problem, NTSB investigator Mike Flanigon told reporters Monday night.

A southbound Yellow Line train stopped about 800 feet beyond the platform at the L'Enfant Plaza station, Flanigon said. A few hundred feet beyond where it halted, "there was an electrical arcing event" involving the electric third rail that powers the train and supply cables leading to that rail, he said.

Portions of both the Green and Yellow lines were shut down so officials could investigate Monday. Following the incident, all Yellow Line service was replaced with additional Blue Line trains.

(Los Angeles Times staff writer Matt Pearce contributed to this report.)

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