The National Transportation Safety Board is expected to take months to complete its investigation of last month's Washington Metro train crash, but it signaled strongly this week that it has already identified the major culprit in the collision.
According to a New York Times story, the NTSB issued an "urgent recommendation" on Monday to the Federal Transit Administration, urging them to tell transit operators nationwide to inspect for a train-detection issue in computerized systems.
It appears that the NTSB is concerned that a single circuit, designed to detect the presence of a train on a given segment of track, may have briefly failed, causing the train to become invisible to Metro's computerized control system. Compounding this problem was an alleged lack of redundancy in safety systems. The NTSB's recommendation thus urges transit operators to ascertain how their systems would react to a loss of train detection, and to investigate whether there are adequate redundant safeguards for such a situation. The suggestion of a single point of failure in the DC Metro crash stands in contrast to Metro's representations immediately after the crash. The Times article notes Metro's original contention that only a case of "multiple system failures" could have caused the collision. NTSB has specifically asked Metro to develop backup systems to help determine when a train's location may be lost by the system, and to respond appropriately.