THIRD UPDATE ON NTSB INVESTIGATION INTO COLLISION OF TWO
METRORAIL TRAINS IN WASHINGTON, D.C.

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The National Transportation Safety Board continues to make
progress in its investigation of the June 22, 2009,
collision of two Washington Metropolitan Area Transit
Authority (WMATA) trains on the Red Line in Washington, D.C.
The Board has developed the following factual information:

Two signal companies, Ansaldo STS USA (US&S) and Alstom
Signaling Inc. (GRS), that designed and manufactured the
automatic train control components for the WMATA system, are
providing technical assistance to the NTSB investigation.

As previously reported, an impedance bond (#15) for the
track circuit where the accident occurred was replaced on
June 17th, 2009, five days before the accident. Continued
review of the maintenance logs has identified that the
impedance bond (#14), located on the other end of the same
circuit, was replaced in December 2007. WMATA records reveal
that this track circuit's train occupancy signal has been
intermittently fluctuating since the replacement was
installed in December 2007. 

The NTSB has requested trouble tickets for the last 18
months to see if these problems had been reported, and
seeking records to see if any operators reported problems on
this circuit.

The investigation is identifying possible sources of
interference affecting the automatic train control (ATC)
operation. These potential sources include Electromagnetic
Interference (EMI), traction power harmonics and signal
crosstalk, communication lines, and system upgrades and
changes.

Following the accident, WMATA began to review operations
data and identified some problems at other circuits. These
anomalies are being examined by NTSB and WMATA to determine
if they are the same kinds of problems as were found in the
location of the accident site.

Testing has identified that the circuit problems are
occurring more frequently during the rush hour time period.
As a result, the NTSB and WMATA testing at the accident
location on the Red Line is continuing. These tests may
result in occasional delays on the Red Line in the Fort
Totten area. All testing in the Fort Totten area is closely
coordinated with WMATA and is scheduled to minimize delays
on that area of track during rush hour.

On Saturday, July 18, the NTSB conducted a sight distance
test at the accident location. Information collected from
the test will be correlated with rail markings documented
after the accident, the braking characteristics of the
striking train, and the speed information gleaned from the
WMATA Operations Control Center records.