Bay Bridge (San Francisco–Oakland)

The San Francisco–Oakland Bay Bridge, commonly known as the Bay Bridge, is a complex of bridges spanning San Francisco Bay in California, connecting San Francisco to Oakland via Yerba Buena Island. As part of Interstate 80 and the direct road between San Francisco and Oakland, it carries about 260,000 vehicles a day on its two decks. Designed by Charles H. Purcell and built by American Bridge Company, it opened on Thursday, November 12, 1936, six months before the Golden Gate Bridge. The bridge's design combined three different types of bridge-building technology over the five miles it covers between San Francisco and Oakland — a suspension span, a cantilevered truss span, and a tunnel — and at the time of its completion was among the longest steel high-level bridges in the world. It is the region's workhorse bridge, carrying more than a third of the traffic of all of the state-owned bridges in the Bay Area combined. Following the 1989 Loma Prieta earthquake, the original eastern cantilever truss span was replaced with a new self-anchored suspension bridge that opened on September 2, 2013, making the bridge's eastern section an entirely new structure engineered to withstand major seismic events.

Background and early proposals

Ever since the Gold Rush days of the 1850s, San Francisco Bay area residents and businesses had lobbied for a bridge joining San Francisco and Oakland. The idea of a bridge linking San Francisco with the cities of Oakland, Berkeley, and Alameda can be traced to 1850, when San Francisco journalist William Walker proposed construction of a causeway, similar to the 2,000-foot Clay Street wharf. Later, railroad executives who had built the western portion of the transcontinental railroad — completed in 1869 — considered the idea, but this concept, regarded as premature given the considerable engineering challenges involved, never advanced.

Perhaps no figure in early Bay Bridge advocacy is more colorful than "Emperor" Joshua Abraham Norton, San Francisco's self-proclaimed eccentric monarch. On August 18, 1869, Emperor Norton issued a proclamation ordering construction of what are now called the Golden Gate Bridge and the San Francisco–Oakland Bay Bridge. Emperor Norton maintained a "summer capital" in Oakland, and as one highway historian pointed out, his bridge proclamation was his "most outstanding proclamation" — the only one that would, eventually, be carried out.

The practical need for the Bay Bridge became undeniable during the 1920s, when automobile registrations and population increased dramatically across the Bay Area. Advancing technology coupled with the rise of the automobile made building a bridge to connect Oakland and San Francisco a financial and technical possibility for the first time. The bridge needed to span more than five miles — four of which are over open water — from Oakland to San Francisco, and be able to withstand turbulent tides, strong salt-laden winds, and potentially devastating earthquakes.

Construction and engineering

The San Francisco–Oakland Bay Bridge began construction on July 9, 1933. The bridge was considered an engineering marvel from its inception, requiring innovations in suspension bridge design that had not previously been attempted at this scale. To meet the considerable engineering challenges, the Toll Bridge Authority and the Department of Public Works appointed Charles H. Purcell as the project's Chief Engineer, Charles Andrew as Bridge Engineer, and Glenn Woodruff as Engineer of Design.

The double-deck crossing extends approximately 8 miles (13 km) in total and consists of two end-to-end suspension bridges with 2,310-foot (704-metre) main spans and 1,160-foot (354-metre) side spans; an exceptionally large-bore tunnel through Yerba Buena Island extending about 0.5 mile; a cantilever bridge with a main span of 1,400 feet (427 metres); and a long viaduct to the Oakland shore. The greatest single challenge in the construction of the Bay Bridge was the sinking to bedrock — some 265 feet below the surface — of the central anchorage for the two suspension bridges. This feat was accomplished through the use of a multiple-dome caisson invented by engineer Daniel Moran.

American Bridge Company erected a total of 167,100 tons of structural steel for the project, including 19,100 tons of air-spun main cables. The western suspension bridges have a suspended length of 9,271 feet and four steel towers rising to a height of 515 feet above the water. Pier E-3, near Yerba Buena Island, had the distinction of being the deepest bridge pier ever built up to that time, at a depth of 242 feet below water level.

The workforce of more than 8,000 who built the bridge accomplished what many engineers had thought was impossible — spanning the full width of San Francisco Bay to provide a critical link between two of California's largest cities. Construction took a little over three years and was completed six months ahead of schedule and under budget, at a total cost of approximately $77 million. The San Francisco–Oakland Bay Bridge was the longest bridge crossing over water and the most costly bridge of its time, with construction made possible in part through the use of compressed-air flotation caissons.

Opening and early history

The bridge opened on November 12, 1936, at 12:30 p.m. In attendance were former U.S. President Herbert Hoover, Senator William G. McAdoo, and Governor of California Frank Merriam. Governor Merriam opened the bridge by cutting gold chains across it with an acetylene cutting torch. Hundreds of fishing boats, yachts, and watercraft passed under the bridge in what was described as "the greatest marine parade San Francisco ever has witnessed." The first person to drive across the bridge was William McCarthy, an aide to then-Mayor Angelo Rossi.

A four-day festival celebrated the finished bridge with parades and fireworks. Thousands eager to cross the bridge caused the biggest traffic jam in San Francisco's history to date, a preview of the congestion the structure would come to define for generations of Bay Area commuters.

The bridge originally carried automobile traffic on its upper deck, with trucks, cars, buses, and commuter trains on the lower. After the Key System abandoned its transbay rail service on April 20, 1958, the lower deck was converted to carry road traffic as well, with vehicles traveling in each direction on a dedicated deck.

In 1956, the American Society of Civil Engineers selected seven engineering wonders of the modern world and named the San Francisco–Oakland Bay Bridge as one of these wonders.

Structure and layout

The bridge has two sections of roughly equal length. The western section, officially known as the Willie L. Brown Jr. Bridge — named after former San Francisco Mayor and California State Assembly Speaker Willie L. Brown Jr. — connects downtown San Francisco to Yerba Buena Island. The eastern section connects the island to Oakland. The two sections are linked by the Yerba Buena Tunnel, bored through the island's central hill, which at the time of its construction was the largest-diameter bore tunnel in the world.

The western section is a double suspension bridge with two decks: westbound traffic is carried on the upper deck while eastbound traffic travels on the lower. The state legislative resolution naming the western section the "Willie L. Brown, Jr., Bridge" passed the California Assembly in August 2013 and the California Senate in September 2013. A formal ceremony was held on February 11, 2014, marking the resolution and the installation of signs on either end of the section.

The eastern section, rebuilt and opened in 2013, is a self-anchored suspension bridge carrying traffic on a single deck. With a width of 258.33 feet (78.74 m) comprising ten general-purpose lanes, it is recognized by Guinness World Records as the world's widest bridge.

During morning commute hours, traffic congestion on the westbound approach from Oakland frequently stretches back through the MacArthur Maze interchange at the east end of the bridge and onto three feeder highways. Since the number of lanes on the eastbound approach from San Francisco is structurally restricted, eastbound backups are also common during evening commute hours.

The 1989 earthquake and eastern span replacement

On the evening of October 17, 1989, during the Loma Prieta earthquake, which measured 6.9 on the moment magnitude scale, a 50-foot section of the upper deck of the eastern truss portion of the bridge at Pier E9 collapsed onto the deck below, indirectly causing one death. The bridge was closed for one month as construction crews removed and rebuilt the fallen section. It reopened on November 18, 1989, with a strengthened repair in place — but the event made clear that the original eastern span would require far more extensive seismic work.

After extensive engineering and political debate over whether to retrofit or replace the damaged eastern span, Caltrans determined that a total replacement was the safest and most cost-effective long-term solution. The original estimate for a seismic retrofit had been approximately $250 million; that figure ultimately gave way to full replacement. Reconstruction of the eastern section as a skyway causeway connected to a self-anchored suspension bridge began in 2002. The new eastern section opened on September 2, 2013, at a reported total cost of more than $6.5 billion, making it the most expensive public works project in California history at the time of its completion.

The new self-anchored suspension bridge was engineered using technology designed to isolate structural damage and allow the main tower to remain standing during a major earthquake. It was designed to withstand the largest potential seismic event expected to occur within a 1,500-year period. Demolition of the old east span was completed on September 8, 2018. Seismic retrofit of the West Span was completed separately in 2004.<ref>{{cite web |title=The Loma Prieta Earthquake Inspired Major Resilience Efforts |url=https://www.spur.org/news/2024-10-17/loma-prieta-earthquake-inspired-major-resilience-efforts-today-need-invest-0 |work=SPUR |date