Golden Gate Update

A comprehensive seismic retrofit is under way to ensure that San Francisco’s 2.74-km-long Golden Gate Bridge will remain in operation even after a maximum credible earthquake of magnitude 8.3 on the San Andreas Fault. The retrofit is divided into three phases. In phase 1, currently under construction, the five independent spans of the north approach viaduct are being connected to create one continuous truss. Large expansion joints are being constructed at each end of the approach, and the four steel support towers are being replaced. The use of isolation bearings significantly reduces the scope of the work that must be done within the truss itself. In phase 2 the retrofit will extend to the south approach, including Fort Point arch, pylons S1 and S2, and the south anchorage housing. Phase 3 will address the retrofit of the suspension portion of the bridge, including the signature span towers. The total cost of construction is estimated to be about $300 million. The work also includes a plan to protect the habitat of the Mission Blue butterfly, a federally listed endangered species.