Cypress Street Viaduct

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Portion of the collapsed Cypress Street Viaduct after the Loma Prieta Earthquake

The collapsed Cypress Street Viaduct seen from ground-level. Note detachment of upper vertical elements from lower and the lack of reinforcement at the point of detachment.

The Cypress Street Viaduct was a 2-kilometer long, raised two-tier, multi-lane (five lanes per deck) freeway constructed of reinforced concrete that was originally part of the Nimitz Freeway (State Highway 17, and later, Interstate 880) in Oakland, California. It replaced an earlier single-deck viaduct constructed in the 1930s as one of the approaches to the San Francisco-Oakland Bay Bridge. It was located along Cypress Street between 7th Street and Interstate 80 in the West Oakland neighborhood. It officially opened to traffic on June 11, 1957 and was in use until the Loma Prieta Earthquake occurred on October 17, 1989 when much of the upper tier collapsed onto the lower tier resulting in 42 fatalities.

When in use, the upper tier was used by southbound traffic, and the lower tier was used by northbound traffic. Some sections of the Cypress Street Viaduct were largely supported by two columns on either side, but some sections were only supported beneath by a single supporting column. The design was unable to survive the earthquake because the upper portions of the exterior columns were not tied by reinforcing to the lower columns, and the columns were not sufficiently ringed to prevent bursting. At the time of its design such structures were not analysed as a whole, and it appears that large structure motion contributed to the collapse. It was built on filled land, which is highly susceptible to soil liquefaction during an earthquake and exhibits larger ground motion.

The viaduct was torn down, and the corridor became known as Mandela Parkway (in honor of Nelson Mandela) with a landscaped median where the viaduct once stood. The Nimitz Freeway was rerouted to loop around the area using a more conventional single level viaduct design.

During construction of the new section of the Nimitz Freeway, a team of archaeologists made many interesting discoveries about the people who lived in West Oakland in the 19th century.^[1]