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Metro officials said the malfunction that appears to be at the heart of last 
month's deadly Red Line crash was traced to "flickering" in a track circuit 
that seemed to be a "freak occurrence" they had never before encountered or 
knew was possible, The Washington Post reports.

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 were 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.