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Agencies Urged to Check Rail Systems for Design Anomaly
The safety board did not say why the errant signals were occurring.
Federal safety officials said the testing and investigation "have raised concerns about how routine track circuit adjustments and/or changes in the operating characteristics of electronic components" in the train control systems "may affect system performance."
Five days before the accident, a Metro crew replaced a key piece of equipment, known as an impedance bond, in the track circuit at the accident site. The replacement of the bond required the track circuit signal strength to be adjusted to accommodate the new equipment, investigators said. It is possible that adjustments made could have inadvertently affected components elsewhere. The track circuit began malfunctioning, or "fluttering," after the equipment was replaced, Metro maintenance records show.
Much of Metro's track components are original equipment manufactured and installed when the Red Line was built in the 1970s. The agency is in the process of upgrading that equipment.
Metro officials said they were taking all measures to make the rail system as safe as possible.
"The NTSB has identified a symptom of the problem with the track circuit, but not a root cause or a solution," said Metro General Manager John B. Catoe Jr. Catoe said Metro will "implement immediately" the board's recommendations to look for errant signals elsewhere and to make sure all electronic components are performing properly.
He said Metro is already working with equipment manufacturers to address concerns raised earlier by the safety board.
Since the crash, Metro has been conducting more rigorous testing of its track circuits.
In July, the safety board said the track circuit electrical system designed to prevent crashes is inadequate and urged the transit agency to add a real-time, continuous backup that would alert train operators to potential problems and stop trains when necessary.
The agency has been in talks with an Annapolis-based company that has a $15 million contract with Metro to provide electronics for the agency's backup operations control center in suburban Maryland and upgrade equipment at the main downtown control center.
The firm, ARINC, is a transportation communications and engineering systems firm. The two sides have been in active talks about estimates for the work, according to Metro spokeswoman Lisa Farbstein.
Metro spokeswoman Angela Gates said crews are still working on replacing the track circuit at the accident site at Fort Totten. She said they're "doing additional testing," but didn't know when the work might be completed.
Staff writer Lyndsey Layton contributed to this report.