October 30, 2012 > BART to adopt earthquake early warning system
BART to adopt earthquake early warning system
Submitted By BART
Thanks to assistance from the Berkeley Seismological Laboratory, the San Francisco Bay Area Rapid Transit system can now automatically brake trains when earthquakes threaten to rattle the Bay Area, allowing perhaps tens of seconds to a minute for trains to slow down before the ground starts to shake.
Implemented in August, 2012, the earthquake early warning system was created with the help of University of California, Berkeley, seismologists who hooked BART into data flowing from the more than 200 stations of the California Integrated Seismic Network throughout Northern California.
Electronic signals from seismic stations travel much faster than seismic waves. For quakes outside the Bay Area, these data give BART's central computers advance notice that shaking is on the way; for quakes in the Bay Area, it provides more rapid warning. If the messages from the seismic network indicate ground motion above a certain threshold, the central computers, which supervise train performance, apply what BART calls "service" braking, which is a normal slowdown to 26 miles per hour. The further the quake from the Bay Area, the more time trains have to slow from speeds up to 70 mph.
"The earthquake early warning system will enable BART to stop trains before earthquake shaking starts and thereby prevent derailment and save passengers from potential injuries," said BART Board President John McPartland. "We are the first transit agency in the United States to provide this early warning and intervention."
BART's Computer Systems Engineering Manager Kevin Copley and UC Berkeley seismologist Peggy Hellweg discussed plans for a broader early warning system along the Pacific Coast that would rival Japan's well-known earthquake early warning system which not only slows trains but alerts schools and can even automatically close valves at industrial sites.
BART has long had accelerometers - devices that detect strong ground movement - in place along the tracks. They sound an alarm bell in the Central Control Facility when the local shaking exceeds a specific threshold. Supervisors then decide whether to radio train operators and tell them to initiate emergency braking to a full stop.
A year ago, BART adopted automatic service braking when the system's own shake sensors detect ground movement. That only works when shaking reaches the BART system, however. The new system gives warning as soon as shaking is detected by remote sensors which can be sooner because of the time it takes for the strong shaking to radiate from the epicenter.
"We're now taking the person out of the loop; so for an earthquake right under the BART system, we have an immediate initiation of braking without anybody having to think," Copley said. "It's a faster response than we would have otherwise."