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The National Transportation Safety Board has identified a cause of the Washington, D.C. Metro crash that killed nine people last month, reports the Washington Post’s Lena H. Sun:

Metro’s automatic train control system relies on track circuits to maintain a safe distance between trains. The circuit detects the presence of trains by using audio frequencies transmitted between the train and the steel rails. The system is supposed to automatically transmit signals to the next train down the line. If the following train gets too close, the system sends a "zero" speed signal that forces it to stop.

Federal investigators and Metro officials said the track circuit where the crash occurred intermittently lost its ability to detect a train after a key component was replaced five days before the crash. Shortly after that repair work, the circuit fluttered and flickered, reporting the presence of a train one moment but not the next, transit officials said.

Washington Metropoliant Area Transit Authority officials claim they will have to "invent" new back-up circuits and, besides, there’s not really the funding for additional safety measures.

Understanding Government did a full report on "WMATA" (just to the right and a little above this post) and found that while it’s a pastime to complain about the Metro trains, the system is usually safe and efficient. The Post has diligently documented the D.C. Metro’s problems since the June 22nd crash. But I think commuters in D.C. and cities with public transit across the country should keep in mind that riding mass transit remains far safer than driving a car.-MB

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