Wednesday, September 23, 2009

Metrorail signal failure prompts NTSB safety recommendations

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The National Transportation Safety Board (NTSB) late Tuesday issued nine safety recommendations, six of which are “urgent,” to address concerns about the safety of train control systems that use audio frequency track circuits following results so far of NTSB's ongoing investigation into the collision between two Washington Metropolitan Area Transit Authority (WMATA) trains in Washington, D.C., on June 22.

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NTSB said it 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.

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, where the accident occurred, to examine the WMATA track circuits and work together to eliminate adverse conditions that could affect the safe performance of these systems. NTSB also called upon WMATA to develop a program to periodically determine that the electronic components in its train control systems are performing within design tolerances.

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Although NTSB stressed that the investigation is not yet complete and no determination of probable cause has been reached, it is concerned about the safety of train control system circuitry used in comparable rail and transit operations in other parts of the country. It has 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.

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 NTSB 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 o the heads of each organization with a request for a response from each organization within 30 days on the urgent ecommendations, addressing the actions taken or planned in esponse to the Board's recommendations.
 
The safety recommendation letter to WMATA may be found at http://www.ntsb.gov/recs/letters/2009/R09_15_16.pdf.

The safety recommendation to Alstom Signaling, Inc., may be found at http://www.ntsb.gov/recs/letters/2009/R09_23.pdf.

The safety recommendations letter to FTA may be found at http://www.ntsb.gov/recs/letters/2009/R09_17_18_19.pdf.

The safety recommendation letter to the FRA may be found at http://www.ntsb.gov/recs/letters/2009/R09_20_21_22.pdf.