The Bay Bridge is a 7-km / 4.5-mile-long bridge connecting San Francisco with Oakland across the San Francisco Bay. The double-deck bridge was completed in 1936, just six months before the opening of the more famous Golden Gate Bridge.
As early as in the nineteenth century, plans were devised to build a bridge across the bay between San Francisco and Oakland. The many technical obstacles and engineering challenges that the construction of a bridge over such a long distance posed – not to mention the financial aspect – meant that the plans were shelved until the 1930s.
Construction eventually started on July 9, 1933, and the bridge was completed just three and a half years later. The bridge had two decks, with the upper deck reserved for vehicular traffic while the lower deck was used by trains. Unfortunately, due to increasing car traffic the train tracks on the lower deck were removed, and both decks were opened to vehicular traffic.
After the bridge was damaged in 1989 during an earthquake that measured 6.9 on the Richter scale, the eastern section of the bridge was completely rebuilt to make it seismic proof. Construction of this new eastern span started in 2002.
The San Francisco – Oakland Bay Bridge, designed by civil engineer Charles H. Purcell, was not only the longest bridge ever built when it opened in 1936, it was also the most expensive with a total cost of $77,600,000.
The bridge has a total length of 4.46 miles (7.18 kilometers) and consist of two sections that are connected by a tunnel – 58 feet high and 76 feet wide (18 x 23 meters) – at Yerba Buena Island. Due to the different characteristics of the soil and water depth on either side of the island, Purcell came up with two distinctly different designs: the western section near San Francisco is a suspension bridge with tall towers and long spans while the eastern section originally had a truss-cantilever design supported by more than twenty pylons. This east section was later replaced by a single suspension bridge and a long viaduct. The west span towers have a height of 519 ft. (158 m.). The modern tower at the rebuilt eastern span is even taller and reaches a height of 525 ft. (160 m).
The two decks have a width of 57.5 feet (17.5 meters), and allow for five lanes in each direction. Traffic in the west direction, towards the city, uses the upper deck and the traffic towards Oakland uses the lower deck.
Eastern Span Replacement
In 1989 the Bay Bridge was closed off for a month after a section of the upper deck of the eastern span collapsed during the Pietra Loma Earthquake, killing one person. Proposals were soon submitted to make the eastern span earthquake resistant, eventually leading to the conclusion that the most cost-efficient solution would be a complete reconstruction of the section between Oakland and Yerba Buena Island.
After an initial design was dismissed for its banal appearance, a contest was held for the design of a long signature span. Meanwhile, construction of the approach to the span – a 1.2-mile-long (1.9 km.) concrete viaduct dubbed the ‘skyway’ – had already started in 2002 just north of the existing bridge. Several years later, the design for the main span was finally approved. Construction of the SAS started in 2006 and the new bridge reopened in September 2013, after which the old eastern span was demolished. This 1,263-foot-long (385 meters) steel span, known as SAS (Self-Anchored Suspension) is now the world’s longest single-tower, self-anchored suspension bridge.