In a recently released advisory, the National Transportation Safety Board (NTSB) cited recent fact finding regarding the collision of two Washington Metropolitan Area Transit Authority (WMATA) trains on June 22, 2009. When an approaching train failed to brake and crashed into a train on the track ahead, there were nine fatalities and numerous serious injuries. An impedance bond for the track circuit was replaced on June 17, 2009 just five days before the crash. Transit authority records indicate that train occupancy signal of the track in question had been fluctuating intermittently since a replacement was installed in December 2007. The investigation is attempting to identify possible sources of interference that could affect the automatic train control (ATC) operation. These include electromagnetic interference, traction power harmonics and signal crosstalk, communication lines, and signal upgrades and changes. On Saturday, June 18, the TSB conducted a sight distance test at the accident location. Information from that test will be correlated with rail markings documented after the accident, the braking characteristics of the striking train, and the speed information obtained from the WMATA Operations Control Center records.View the NTSB Advisory online.
EMI Cited as One Possible Factor in Deadly DC Metrorail Crash
