Agencies Urged to Check Rail Systems for Design Anomaly
Wednesday, September 23, 2009
Federal investigators issued urgent safety recommendations nationwide Tuesday about the train control system at the center of the fatal Metro crash in June.
The investigators, while not pinpointing a cause for the crash, say a possible design anomaly in an automated control system could have allowed it, raising serious concerns about the safety of Metro and all other transit systems with the same technology. Investigators also raised concerns about how routine maintenance could have affected the performance of the system.
Metro and other transit agencies should examine their train control systems, in cooperation with the manufacturer, to guard against further malfunctions, the agency said.
The National Transportation Safety Board sent advisory letters with the recommendations to Metro, the Federal Railroad Administration, the Federal Transit Administration and Alstom Signaling, the company that makes the train protection equipment.
"After only three months, this complex investigation is far from complete, so we are not ready to determine the probable cause of the accident," 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 [Metro] or another transit or rail system."
Investigators said errant signals emitted from equipment in a train control room near the site of the Fort Totten crash gave a false signal to the automated crash-avoidance system, erroneously telling it the track was clear when in fact it was occupied by an idling train. As a result, the track circuit system that is supposed to prevent crashes failed to detect the train and did not send signals to slow or stop the approaching train. Nine people were killed and 80 injured in the June 22 accident.
A spokesman for the Federal Railroad Administration, which oversees about 700 railroads, said it was not immediately clear how many or which rail systems use the same type of track circuits. Industry officials said relatively few railroads are affected.
Among transit agencies, Boston, Atlanta, Philadelphia, San Francisco and Baltimore are the major cities with similar track circuitry controls. Spokespeople for several transit agencies said they needed time to review the recommendations.
In the letters, safety board officials said the accident investigation "has raised concerns about the susceptibility of this audio frequency track circuit design to errant signals."
The Metro system relies on track circuits to maintain a safe distance between trains. The circuit system detects the presence of trains using audio frequencies transmitted between the train and the steel rails and automatically transmits signals to the next train down the line. If the following train gets too close, the system sends signals that force it to slow or stop.
The safety board also called on Metro to develop a program to periodically determine that the electronic components in the train control systems are performing properly.
The board urged Alstom to help Metro and other transit agencies examine the train control systems for vulnerability to the false signals. An Alstom spokeswoman did not return a telephone call.