A new earthquake early-warning system installed by Bay Area Rapid Transit will detect earthquakes precious seconds before the ground starts shaking, allowing trains to be slowed down in an effort to prevent derailments.
The system was designed with the help of University of California, Berkeley scientists and is similar to one already being used in Japan that was instituted last month.
State and federal quake scientists already have installed a series of 200 sensors from central California to the Oregon border, and BART's new early warning system taps into this array, called the California Integrated Seismic Network.
Richard Allen, director of the Berkeley Seismological Laboratory, said BART's system is "a key step forward in our development of an early warning system for the U.S."
If a 5.0-magnitude-or-stronger quake hits far away, or a 4.0 closer to the San Francisco Bay area, the early-warning system sends an alarm to BART's central computers, which can slow trains by about 2 miles per hour per second.
Electronic signals travel much faster than seismic waves, so BART's computers can get advance notice that ground movement is on the way and start slowing trains to be slowed to 26 mph.
The system carries about 400,000 riders a day to destinations on 104 miles of track.
Carlton Allen, BART's chief engineer, told the San Jose Mercury News that a train travelling at 72 mph could be slowed to 32 mph in 20 seconds after receiving a warning.
"We're in earthquake country. If we can buy time, why shouldn't we?" he told the paper.
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