National Transportation Safety Board Member Debbie Hersman today, testifying before Congress, described a multi-faceted National Transportation Safety Board investigation into the deadliest accident in the history of the Washington Metropolitan Area Transit Authority (WMATA). A collision between two trains on June 22 killed 9 people and injured scores of others.
At a hearing before the Subcommittee on Federal Workforce, Postal Service and the District of Columbia, Committee on Oversight and Government Reform, Hersman noted that within hours of hearing about the collision, the Safety Board dispatched a team of investigators from its headquarters in Washington and from regional offices in Illinois and California.
Although the investigation continues, Safety Board investigators have concerns about the safety redundancy of WMATA's automatic traincontrol system, Hersman said. The accident demonstrated that the system is susceptible to a single point failure because it did not stop a train when detection of a preceding train was lost, she said.
"Automatic train control systems are supposed to detect the presence of all trains at all times," Hersman said, "but in the unfortunate event that the system fails, there should be a built-in safety redundancy, like a real-time alert, to prevent trains from hitting one another."
Hersman noted that the Safety Board issued two urgent safety recommendations yesterday to address the issue. One safety recommendation asks WMATA to evaluate track occupancy data on a real-time basis in order to detect losses in track occupancy and automatically generate alerts to prompt actions to avoid collisions, such as stopping train movements or implementing speed restrictions, Hersman said. The other safety recommendation asks the Federal Transit Administration to advise all rail transit operators with similar train control systems to determine whether their system has adequate safety redundancy in the event of a loss of train detection, and if not, to take corrective action.
"Our investigation of this accident is far from completed," Hersman said, "but the presence of safety redundancies for those times when an automatic train control system loses detection of a train is a critical issue, not just for Metrorail, but perhaps for transit systems across the country."