WASHINGTON — The National Transportation Safety Board issued an “urgent safety recommendation” to the Washington Metropolitan Area Transit Authority (WMATA) calling for enhanced safety redundancy of its train control system.
“A recent accident on the Metrorail’s Red Line between the Fort Totten and Takoma stations has shown that WMATA’s train control system is susceptible to a single point failure because it did not fail safe and stop a train when detection of a preceding train was lost,” they NTSB said in a statement. “The urgent safety recommendation issued today calls for 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 such actions as immediately stopping train movements or implementing appropriate speed restrictions to prevent collisions.”
The Safety Board made a second urgent 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.
Although the NTSB’s investigation is not yet complete and no determination of probable cause has been reached, investigators have concerns regarding the safety redundancy of WMATA’s train control system.
“While the NTSB is still in the very early stages of its investigation into this tragic accident here in our nation’s capital,” said Acting Chairman Mark V. Rosenker, “we have concerns about the failure of WMATA’s train control system to prevent this collision. 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.”
In accordance with 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.
“In spite of the issuance of this recommendation, the NTSB still has not determined the root cause of the accident. Every component of that circuit has been replaced, but the problem still persists,” WMATA said in a statement. “This is not a simple problem as is evidenced by the NTSB’s statement that ‘investigators are continuing to examine the train control system circuitry and recorded data to better understand how the train control system functioned prior to the accident.’
“It is important to know that there are currently no systems available commercially that could provide the Metro system with the kind of alerts that the NTSB has recommended, and that such a system must be invented. San Francisco’s Bay Area Rapid Transit system for example, would not meet our unique needs,” WMATA said. “We believe the NTSB acknowledged this much in its letter today, stating, ‘The NTSB believes that software algorithms or additional circuitry could be developed to continuously evaluate the validity of real-time track occupancy data and alert operations personnel when problems are detected.'”
As a result, WMATA said it “will be developing a new system that will be specifically tailored to Metro. Metro is in the process of contacting vendors who have the expertise needed to help us develop this service, and we are preparing cost estimates on this application.”