San Francisco – Oakland Bay Bridge

The San Francisco Oakland Bay Bridge spans the bay with a double-deck steel structure that changes from a suspension span to a cantilever truss midway across. It opened in nineteen thirty-six, six months before the Golden Gate Bridge, but it handled the massive flow of regional traffic between two cities. During the nineteen eighty-nine Loma Prieta earthquake, a segment of the upper deck collapsed onto the lower deck. That failure forced engineers to rethink the safety of the entire connection for years.