page_title: History of Bay Area Rapid Transit
section_title: Earthquake safety
hierarchical_section_title: History of Bay Area Rapid Transit / Silicon Valley extension (2009–present) / Earthquake safety
caption_attribution_description: English: The El Cerrito del Norte (BART station) in El Cerrito, California, USA. This steel reinforced concrete pylon is in the process of being wrapped in fiberglass and refinished as part of a seismic retrofit upgrade of the BART line.
context_page_description: Bay Area Rapid Transit, widely known by the acronym BART, is the main rail transportation system for the San Francisco Bay Area. It was envisioned as early as 1946 but the construction of the original system began in the 1960s.
context_section_description: Despite the robustness of the system following the 1989 Loma Prieta quake, a 2010 study showed that BART overhead structures could collapse in a major earthquake, which has a significant probability of occurring within three decades. Seismic retrofits were necessary to address these deficiencies, although one in particular, the penetration of the Hayward Fault Zone by the Berkeley Hills Tunnel, will be left for correction after a large earthquake.
  An earthquake early warning system called ShakeAlert, sponsored by the United States Geological Survey, was instituted in 2012 with the help of UC Berkeley seismologists who linked BART to 200 stations of the California Integrated Seismic Network. These electronic signals travel much faster than seismic waves. For quakes outside the Bay Area, they provide advance notice that shaking is on the way; for quakes in the Bay Area, they provide an earlier warning. If the seismic network warns of ground motion above a threshold, the train control computers will order “service” braking, slowing from normal speeds of up to 70 miles per hour (110 km/h) to 26 miles per hour (42 km/h) .
  “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.”
  The 3.6-mile (5.8 km) Transbay Tube has also required earthquake retrofitting. The immersed tube lies in a shallow trench dredged on the bottom of San Francisco Bay, and was anchored to the bottom by packing around the sides and top with mud and gravel. This fill may be prone to soil liquefaction during an earthquake, which could allow the buoyant hollow tube to break loose from its anchorages. Retrofitting outside the tube compacted the fill, to make it denser and less prone to liquefaction. Inside the tube, BART installed heavy steel plates, to reduce sideways movement in an earthquake. The work was performed between March and December 2013, and BART closed one of the two bores of the tube early on some weeknights. Trains shared a single tunnel between Embarcadero and West Oakland after 10 pm, with travel delays of 15–20 minutes. The work, estimated to take 14 months, was completed after 8 months.
caption: Seismic retrofitting at El Cerrito del Norte station
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