Thanks to assistance from the Berkeley Seismological Laboratory, the San Francisco Bay Area Rapid Transit District (BART) can now automatically brake its trains when earthquakes threaten to rattle the region, allowing time for trains to slow down before the ground starts to shake.

BART worked with seismologists from the University of California, Berkeley, who connected the agency with data from the more than 200 stations throughout Northern California of the California Integrated Seismic Network.

Electronic signals from seismic stations travel much faster than seismic waves, BART explained. For quakes outside the bay area, this data gives BART’s central computers advance notice that shaking is on the way; for quakes in the area, they provide more rapid warning.

If the messages from the seismic network indicate ground motion above a certain threshold, the central computers, which supervise train performance, institute what BART calls “service” braking, which is a normal slowdown to 26 miles per hour. The farther the quake from the bay area, the more time trains have to slow from speeds up to 70 mph.

BART has long had accelerometers—devices that detect strong ground movement—positioned along the tracks. They ring an alarm bell in the Central Control Facility when the local shaking exceeds a specific threshold. Supervisors then would make the decision whether to contact train operators and tell them to initiate emergency braking to a full stop.

A year ago, BART instituted automatic service braking when the system’s own shake sensors detect ground movement; however, this only works when shaking reaches the BART system. In contrast, the new system gives warning as soon as shaking is felt at remote sensors, which can be sooner because of the time it takes for the strong shaking to radiate from the epicenter.

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