Investigators say a signaling system failed to detect a stopped commuter train during tests of the track where a deadly crash occurred this week in Washington, D.C.
The National Transportation Safety Board said Thursday that the train control system lost detection of a test train that was stopped in the same place as the train that was struck on Monday.
The NTSB also says the operator of the struck train was interviewed Thursday. He told investigators that his train was running in manual mode at the time of the crash. The operator says he was waiting for another train to clear when he felt a hard push to his train from behind.
Investigators say they are still examining the crash site to understand how the train control system functioned on Monday.
The Washington-area mass transit system will inspect every stretch of its tracks as federal investigators work to determine whether problems found with a signaling system in one area could have contributed to this week's crash that killed nine people.
Metro General Manager John Catoe also said Thursday the agency will start rearranging its trains to put the oldest and structurally weakest rail cars in the middle, instead of at the ends, where they are more vulnerable.
Catoe said he ordered inspections of all 3,000 circuits, or sections beneath the track that include a signaling system. The signals provide critical information to passing trains such as when to stop or slow down. Tests by the National Transportation Safety Board indicated a problem with one of the circuits in the area of Monday's crash.
'Circuits are vital'
"Whether trains are operated in automatic or manual, these circuits are vital," said Debbie Hersman of the National Transportation Safety Board. "We're particularly interested in the speed commands that might be sent from that circuit when there's a train standing on that circuit."
Investigators were planning to test the track with a six-car train.
An engineering professor who's studied transportation safety said that if sensors failed on the track, it could have contributed to Monday's crash. He emphasized, though, that catastrophic crashes usually can't be blamed on a single factor.
"If the sensors didn't work properly, it deprived (the train operator) of very vital information," said Najm Meshkati, professor of engineering at the University of Southern California. The operator, he said, "was the last layer of defense."
Since the crash, the NTSB has also criticized Metro for failing to revamp or replace its 1000-series rail cars after previous warnings by the agency. The striking train, which sustained most of the damage in Monday's crash, was made up of those cars, which date back to the 1970s. The cars are not as good at withstanding crashes as later models.
Catoe insisted Thursday that the cars were safe, but said the agency was in the process of putting the 1000-series cars in the middle of trains, and not on the ends, as an added precaution. Metro spokeswoman Lisa Farbstein said later it would not be possible to make that change in every case, but the agency will do it where they can.
The union representing Metro workers demanded that change on Wednesday.
Metro on Thursday reopened the two stations that had been closed since the crash, but only for rush hour. Trains were running along just one track, leaving the side damaged in the crash closed as the investigation continues.
Family seeks $950,000 in lawsuit
A Washington couple who say their 15-year-old son was injured in the crash filed a lawsuit in federal court on Wednesday against Metro, which is formally known as the Washington Metropolitan Area Transit Authority.
In the lawsuit, Imhotep Yakub and Dawn Flanagan say their son, Davonne Flanagan, was a passenger in the striking train. They say he fractured his femur and suffered other injuries. The family is seeking $950,000 in damages.
The deadliest crash in the rail system's 33-year history occurred when a train plowed into another that was stopped. The moving train was operating in automatic mode, which means it was primarily controlled by a computer, although there is evidence the operator applied the emergency brake.
Since the crash, trains have been manually controlled as a precaution against computer problems. Catoe said trains will continue running manually until all the circuits are inspected and the agency is "100 percent sure the system is in 100 percent working condition."
Hersman said inspectors found 300 feet to 400 feet of rails that showed signs of emergency braking. Hersman also has said the emergency brake control on the moving train was found pushed down, though it's not clear how or when that happened. The operator of the oncoming train was among the dead.
Hersman said investigators hoped to interview the operator of the other train on Thursday, a day after his release from the hospital.
NTSB officials say their investigations can take more than a year.