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Why a New Bridge?
Earthquakes and Bridges
East Span Design Basics
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Why A New Bridge?

On October 17, 1989, the tremors of the Loma Prieta earthquake signaled the beginning of the end for the eastern span of the San Francisco-Oakland Bay Bridge. The 7.1 quake severely damaged the 1930s-era double-deck truss structure, knocking down a portion of the upper deck, killing one motorist and tragically exposing the span's weakness.

With the bridge out of service for a month, Caltrans inaugurated a study to determine if the bridge could withstand another earthquake. For sure, another quake is coming. Seismic experts say a major temblor is likely to occur in the next 30 years - a ominous finding for the bridge, considering it lies in harm's way just a few miles from the San Andreas and Hayward faults.

Caltrans determined that while the western side of the bridge from San Francisco to Yerba Buena could be retrofitted to withstand a major quake, it would be far more cost-effective in the long run and safer to build a new eastern span rather than retrofit it. Built according to 1930s codes, the bridge was designed for what today are merely minimal seismic impacts. The wooden timbers on which the bridge piers stand leave the bridge increasingly vulnerable over time. To bring the bridge up to modern standards would be relatively too expensive, unreliable and extremely difficult given today's traffic levels.

And while seismic safety is the primary consideration for the new east span, additional traffic safety issues are also important. The existing structure does not conform with current traffic standards. The new east bridge is designed to meet current standards for roadway shoulders, lane widths, stopping sight distances, and other factors, helping to substantially improve public safety.

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