The National Transportation Safety Board (NTSB) continues 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.

According to a press release, the NTSB has developed the following factual information:

To date, significant work has been done to determine why the presence of train 214 was not identified on the train control circuit that allowed train 112 to crash into it. The NTSB's accident investigation is continuing, and more work is needed to fully understand why the train control system did not perform as designed.

Most of the electrical components on this system are original equipment from the mid-1970s. NTSB investigators, along with personnel from WMATA, the Federal Transit Administration, and the equipment manufacturers, are carefully examining all components to understand how any change or degradation in component performance might affect the train control system.

The train control room at Fort Totten Station contains dozens of modules for the track circuits north and south of the station. Investigators have been concentrating on the two track circuit modules for the accident site. Both of these modules contain twenty circuit boards with capacitors, resistors, and transistors. Each of these components is being tested extensively to determine component operating values, tolerances, circuit interactions, and the effect of their performance on the train control system. As part of the process for replacing impedance bonds at the site before the accident, adjustments were made to track circuit signal strength. The investigation is evaluating any effect that these track circuit adjustments may have had on the performance of track circuit modules located at Fort Totten.

The two modules that were in place at the time of the accident were removed from the Fort Totten train control room for examination by the accident investigation team at WMATA's laboratory. Two replacement modules were installed at the Fort Totten station that showed similar anomalies and they were removed and preserved for further testing. Two additional modules were then installed by WMATA at the Fort Totten station that did not display these anomalies.

The NTSB's investigation will continue at the accident site at Fort Totten, at WMATA's laboratory facility in Landover, Md., and at WMATA's Operations Control Center to determine why the automatic train control system failed to prevent the collision on June 22, 2009.