On Monday, the National Transportation Safety Board (NTSB) issued an urgent safety recommendation to the Washington Metropolitan Area Transit Authority (Metro) calling for enhanced safety redundancy of its train control system.

The 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.

The urgent safety recommendation issued on Monday calls for Metro 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 Metro's train control system.

The safety recommendation letter to Metro may be found here.