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Two Washington Metropolitan Area Transit Authority (Metro) six-car Red Line trains collided on Monday, resulting in nine fatalities, including a female train operator, and 76 confirmed injuries, many serious, according to a FEMA report. It is the deadliest accident in Metrorail's 33-year history.

Metro officials are working with the National Transportation Safety Board, which on Tuesday said the trains were recommended for phaseout in 2006.

"This is an incredibly tragic day and our hearts go out to the families of those who suffered fatalities and to those whose loved ones are injured," said Metro GM John Catoe. "We are committed to investigate this accident until we determine why this happened and what must be done to ensure it never happens again."

Metro officials do not yet know the cause of the collision and are not likely to know the cause for several days as the investigation unfolds. Both trains were on the same track headed toward Shady Grove Metrorail station, according to preliminary reports. The female operator was on the trailing train.

In a statement, U.S. Transportation Secretary Ray LaHood said: "This morning I spoke to John Catoe, General Manager of the Washington Metropolitan Area Transit Authority, and offered him any assistance I can provide from the Department of Transportation. My prayers are with the victims of this horrible accident, as well as their families, who have been suffering with them."

Experts are also weighing in on the D.C. crash. For more, click here.

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