For days before Red Line crash, circuit failures left Metro trains invisible
Saturday, July 31, 2010
National Transportation Safety Board investigators this week provided the most detailed, blow-by-blow explanation yet for the June 22, 2009, Metro Red Line crash -- an account of how aged, faulty equipment left trains invisible for days on a stretch of track near the Fort Totten Station, making the crash an accident waiting to happen.
Metro's failure to use an existing test that could have identified the problem and prevented the crash, in which one train slammed into another, killing nine people and injuring scores of others, underscored what the NTSB called the transit agency's weak commitment to safety and spurred calls in Congress for aggressive reforms.
"Congress has to take ownership as well," Sen. Barbara A. Mikulski (D-Md.) said after a briefing on the NTSB report for local congressional delegations Friday. She said Congress should pass legislation to grant the Transportation Department regulatory authority over public transit systems and, in the long run, reform Metro's governance structure.
Mikulski also supported continuing the dedicated federal funding of Metro, such as the $150 million the House and Senate approved this month.
At Tuesday's NTSB meeting, investigators outlined how the crash was caused by a problem with a track circuit module built by General Railway Signal (which was bought by Alstom Signaling) and Metro's failure to detect it.
The track circuit modules, stacked in metal racks in concrete "train control rooms," are part of Metro's automatic train control system.
Metro has about 3,000 such modules, which work by emitting a signal that travels along the rails. When a train is not present, the signal loops around the tracks and returns to the module receiver. If the signal's journey is broken by the wheels of a train, a message is sent to trains behind it to regulate their speeds and stay back.
But in some cases, the electrical signal indicated the tracks were clear without ever running along the rails. On June 17, 2009, key pieces of equipment connected to the module on track circuit 304 near Fort Totten were replaced and the power increased, causing a problem known as "parasitic oscillation," in which the signal jumped directly from the transmitter to the receiver inside the module.
Tests after the accident showed that circuit module wasn't alone. Nearly 300 modules had problems with their electrical signals, and alarms indicating the phenomenon occurred so often that they were ignored as "minor."
Metro had an enhanced test for the loss of train detection that was developed in the wake of a 2005 near-miss close to Rosslyn. But Metro technicians working on the circuit in the days before the crash were not familiar with that test.
For five days, trains zoomed along track circuit 304 undetected, but they were spaced widely enough that they did not collide. On June 22, there was a malfunctioning train on the Red Line that had to be taken out of service, causing trains behind it to become backed up. In addition, the operator of the lead train, No. 214, was using manual mode, in violation of Metro rules, causing it to move more slowly than it would have on automatic.
Train 214 stopped completely within the boundaries of track circuit 304 and was not detected, so speed commands instructed the following train, No. 112, to advance at 55 mph. Because the train was advancing along a bend, the operator could not see the train ahead until it was too late.
The operator applied the emergency brake about three seconds after coming into view of the train ahead, but that only slowed the train a few miles per hour before the two collided.