Sister Transit System Took Steps to Counter Hazard

But that type of transient, intermittent failure is known to experts who work with automated transit systems and was flagged as a hazard by the Bay Area Rapid Transit system in San Francisco. Officials there installed a separate system as a protection against flickering track circuitry.

BART is considered a sister system to Metro because it was built about the same time using similar designs, technology and suppliers. Metro never installed the backup system, known as the sequential occupancy release system, that is used by BART.

Metro's rail chief, Dave Kubicek, said through a spokesman last week that he was not familiar with the BART system. Metro General Manager John B. Catoe Jr. said the flickering circuitry was a "freak occurrence." Like other major subway systems in the United States, Metro's highly automated system is designed to be fail-safe. Metro spokeswoman Lisa Farbstein said that every transit system is unique and that it is difficult to know the "intricacies of everybody else's system and how they compare to ours."

Metro's train protection system relies on track circuits to maintain a safe distance between trains. The circuit 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 a "zero" speed signal that forces it to stop.

Shortly after BART started operating in 1972, it installed a backup system. Initial tests of the main train protection system failed to detect the presence of a train in a few instances, according to Mike Healey, a longtime BART spokesman who retired in 2005. A subsequent 1972 BART accident involving a train that mistakenly received a command to double its speed instead of slowing down, sending the train off track and into a parking lot, was the catalyst "to have some redundancy to back up the primary train protection system," Healey said.

The BART train protection and backup systems were built by Westinghouse. Most of the nation's other subway systems, including Metro, have train protection systems built by General Railway Signal, which was acquired by Alstom, or Union Switch & Signal, which is a unit of Ansaldo STS. Representatives of Alstom and Ansaldo have declined to comment on their contracts with Metro.

In the June 22 Red Line crash, one train ran into the back of another stopped north of the Fort Totten Station in Northeast Washington, killing nine and injuring 80 in the deadliest crash since Metrorail began operating in 1976.

Federal investigators and Metro officials said the track circuit where the crash occurred intermittently lost its ability to detect a train. Five days before the crash, a Metro crew replaced a key component in the track circuit. Shortly after that repair work, the circuit fluttered and flickered, reporting the presence of a train one moment, but not the next, transit officials said. Metro officials said the intermittent failure would not have been obvious in Metro's downtown operations center, where controllers monitor real-time movement of trains by watching an illuminated graphic depiction of the 106-mile system.

The findings by the National Transportation Safety Board suggest that if the circuit was malfunctioning on the day of the crash, the system would not have detected the idling train and would have sent a "clear" signal to the striking train. Onboard computers would have set the train to 59 mph, the speed limit along that stretch. Investigators have stopped short of saying that the malfunctioning circuit caused the crash.

Ron Tolmei, an electrical engineer and former manager of research and development at BART, said he was aware of intermittent failure of track circuits on BART and the Muni light-rail system in San Francisco.

Although he emphasized that he did not know the specifics of the Metro crash, Tolmei said intermittent failure of track circuits most often occurs when there is poor electrical contact between the steel rails and the wheels of the train.

"It's not so much a device

problem as a physics problem," said Tolmei, a principal investigator at Innovation, an engineering firm based in Walnut Creek, Calif.

Rusty rails or some type of film or barrier on the rails can mar the connection between the rails and the wheels, he said. In addition, he said, flickering tends to occur on short blocks, or sections of railroad. The Metro railroad is divided into blocks of varying lengths.

Tolmei invented an alternative backup system in 2006 that would detect flickering in track circuitry and provide the same type of protection as sequential occupancy release but would allow a transit system to more quickly and easily recover from an intermittent failure. Tolmei holds a patent on the system, but it has not been produced commercially.

Willard Wattenburg, an electrical engineer and inventor retired from the University of California at Berkeley, said intermittent failures were frequent on BART in the early 1970s.

Wattenburg analyzed BART's initial design for the California Public Utilities Commission, which regulates transit systems, and crafted some corrections. BART officials at the time said the failures were flukes, but regulators insisted on the design changes.

Staff researcher Meg Smith contributed to this report.