The National Transportation Safety Board Monday issued a safety recommendation to the Washington Metropolitan Area Transit Authority (WMATA) calling for enhanced safety redundancy of its train control system. The call follows the June 22 accident on the Metrorail Red Line between Fort Totten and Takoma stations, which according to NTSB shows the Metrorail train control system is susceptible to a single point failure, which did not “stop a train when detection of a preceding train was lost.”
The NTSB recommendation says WMATA should evaluate track occupancy data on a real-time basis in order to detect losses in track occupancy and automatically generate alerts to prompt such actions as immediately stopping train movements or implementing appropriate speed restrictions to prevent collisions.
NTSB also made a second recommendation to the Federal Transit Administration (FTA) urging the agency to advise all rail transit operators with train control systems capable of monitoring train movements to evaluate their systems for adequate safety redundancy.
"While the NTSB is still in the very early stages of its investigation into this tragic accident here in our nation's capital, we have concerns about the failure of WMATA's train control system to prevent this collision," said Acting Chairman Mark V. Rosenker. “By calling upon WMATA to take swift action to upgrade the safety redundancy of its system and by urging FTA to alert other transit agencies of the hazards of single point failures such as the one experienced by WMATA, we hope to prevent something similar from happening again."
Per NTSB protocol, the letters were issued to the heads of both agencies with a request for a response from each organization within 30 days, addressing the actions taken or planned in response to the Board's recommendation.
The safety recommendation letter to WMATA may be found here.
The safety recommendation letter to the FTA may be found here.