Isn't 'the train was rear-ended' an "explanation of the accident"? Taken from Yahoo's article: "Metro chief John Catoe said the first train was stopped on the tracks, waiting for another to clear the station ahead, when the trailing train plowed into it from behind. Each train had six cars and was capable of holding as many as 1,200 people. Officials had no explanation for the accident. The National Transportation Safety Board took charge of the investigation and sent a team to the site of the worst accident in the Metro system's 33-year history." Other sources: 1) CNN - http://www.cnn.com/2009/US/06/22/washington.subway.crash/index.html 2) MSN - http://www.cnn.com/2009/US/06/22/washington.subway.crash/index.html 3) USA Today - http://www.usatoday.com/news/nation/2009-06-22-metro-collision_N.htm