During the investigation, the NTSB has discovered that a failure occurred in which a spurious signal generated by a track circuit module transmitter mimicked a valid signal and bypassed the rails via an unintended signal path. The spurious signal was sensed by the module receiver, which resulted in the train not being detected when it stopped in the track circuit where the accident occurred.
The NTSB made specific recommendations to the Washington Metropolitan Area Transit Authority and to Alstom Signaling, Inc., the manufacturer of the track circuit modules at the Fort Totten station, to examine the WMATA track circuits and work together to eliminate adverse conditions that could affect the safe performance of these systems. Additionally, the NTSB called upon WMATA to develop a program to periodically determine that the electronic components in its train control systems are performing within design tolerances.
Although the NTSB's investigation is not yet complete and no determination of probable cause has been reached, the NTSB is concerned about the safety of train control system circuitry used in comparable rail and transit operations in other parts of the country. Therefore, the NTSB recommended that the Federal Transit Administration (FTA) and the Federal Railroad Administration (FRA) advise all rail transit operators and railroads that use audio frequency track circuits in their train control systems about these findings from the Fort Totten accident investigation.
The NTSB also recommended that the FTA and FRA have transit operators and railroads that use audio frequency track circuits examine their track circuits and work with their signal equipment manufacturer(s) to eliminate adverse conditions that could affect the safe performance of these systems, and to develop programs to periodically determine that the electronic components in their train control systems are performing within design tolerances.
"After only three months, this complex investigation is far from complete, so we are not ready to determine the probable cause of the accident on WMATA," said Chairman Deborah A.P. Hersman. "However, our findings so far indicate a pressing need to issue these recommendations to immediately address safety glitches we have found that could lead to another tragic accident on WMATA or another transit or rail system."
In accordance with NTSB protocol, the letters were addressed to the heads of each organization with a request for a response from each organization within 30 days on the urgent recommendations, addressing the actions taken or planned in response to the Board's recommendations.