Metro Crash Investigation Turns Up Electronic Control 'Anomalies'
Thursday, June 25, 2009
Federal investigators said yesterday that they found "anomalies" in a key component of the electronic control system along the Metro track north of Fort Totten, suggesting that computers might have sent one Red Line train crashing into another.
A senior Metro official knowledgeable about train operations said an internal report confirmed that the computer system appeared to have faltered.
Investigators stopped short yesterday of saying that the equipment malfunctioned or that it caused Monday's crash, which killed nine people and injured 80. But Debbie Hersman of the National Transportation Safety Board said investigators are looking closely at a 740-foot-long circuit near the crash site that malfunctioned during testing. "These circuits are vital," she said. "It's a signal system. It's providing information, authorization and speed commands to the following train."
Investigators are continuing to run tests, trying to determine whether the circuit failed to detect the train that was idling on the tracks north of the station and was rear-ended by a southbound train shortly after 5 p.m. Monday.
Hersman said investigators are also examining the actions of Jeanice McMillan, the novice operator of the striking train, who was among those killed in the wreck. The steel rails show evidence that McMillan activated the emergency brakes 300 to 400 feet before the pileup, which occurred on a curved section of track between the Takoma and Fort Totten stations, Hersman said.
Last night, investigators planned to run a train similar to the one involved in the crash to test the circuit. In coming days, another simulation will be conducted to determine whether the curve, or anything else, might have obstructed McMillan's view of the idling train.
The speed limit where the crash occurred is 59 mph, the top speed on the Metro system. If the track circuit failed to detect the idling train, computers onboard McMillan's train would have set her train's speed at 59 mph, making it difficult for her to hit the emergency brakes in time to avoid a crash. The impact pushed the idling six-car train forward seven feet, Hersman said. An empty six-car train weighs about 237 tons.
McMillan, 42, had been running trains without supervision for a few months.
Metro's automated trains are controlled by several electronic systems. The train protection system is made up of circuits embedded along the track, anywhere from 150 feet to a half-mile apart. As trains cross the circuits, signals are transmitted down the line to following trains. The signals automatically set speeds, slowing or stopping a train so that it doesn't crash into the one in front.
The railroad is divided into blocks, and the computers are set to keep two blocks of distance between trains. As an added layer of control, another electronic system regulates train speeds and spacing and stops the trains as they enter stations. A third system controls overall train movements to maintain proper routing and keep trains on schedule; it is monitored by workers in Metro's downtown central control room.
If the train protection system is working as designed, when one train begins to enter the two-block buffer behind another, the computers automatically deploy the brakes on the second train and force it to stop.
When investigators used a "shunt," a device that simulates a train on the tracks, to test the six circuits in the stretch near the crash, five worked properly and one did not, Hersman said. Hersman said that maintenance was done on the one circuit this month and last year and that those records will be examined.