NTSB identifies signal failure in fatal D.C. Metrorail collision

The National Transportation Safety Board 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. The recommendations are the result of NTSB's ongoing investigation into the collision between two Washington Metropolitan Area Transit Authority trains on the Red Line near the Fort Totten station in Washington, D.C., on June 22, 2009.

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.