At least seven people are dead and more than 70 are injured after a subway train collision in the Washington, DC, area. A commuter train on DC’s red line, the Metro System’s busiest line, rammed into the back of a stopped train during rush hour on Monday.

While investigators do not know for sure what caused the crash, disheartening information coming to light today draws a dark cloud over the 33-year-old Metro System.

Debbie Hersman, Chairwoman of the National Transportation Safety Board, said in a press conference this morning that the NTSB expressed safety concerns three years ago that thousand-series fleets — which were reportedly involved in Monday’s collision — should be either removed or modified. Hersman said that the Metrorail transit system "was not able to do what we asked them to do" and the old trains kept running.

Yesterday’s collision is being described as the worst accident in the Metrorail’s history. The Metro System, a landmark in the District of Columbia, shuffles business workers, tourists and locals from Washington to Maryland and Virginia suburbs.

As investigators continue to search for recorders from the train that was struck, in hopes they will provide information to help determine why the crash occurred, our hearts and prayers go out to the victims and their families.