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San Francisco–Oakland Bay Bridge
The double-decked bridge across San Francisco Bay
The San Francisco–Oakland Bay Bridge opened on November 12, 1936, six months before the Golden Gate Bridge, and it carries far more traffic, about 260,000 vehicles a day. At about 4.5 miles (7.2 km) between toll plaza and shore, it was among the longest bridges in the world when built. Its western half is really two suspension bridges joined end to end at a central anchorage, and the roadway passes through a tunnel bored through Yerba Buena Island halfway across the bay.
During the 1989 Loma Prieta earthquake, a 50-foot section of the upper deck of the eastern half collapsed onto the deck below, closing the bridge for a month and exposing its seismic weakness. The answer was an entirely new eastern span, a single-tower self-anchored suspension bridge that opened in 2013 at a cost of more than $6.5 billion, one of the most expensive public works projects in California history. The American Society of Civil Engineers named the original Bay Bridge one of the seven wonders of American engineering in 1952.