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.