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First Avenue Bascule Bridge

The First Avenue South Double Leaf Bascule Bridge carries the First Avenue traffic across the Duwamish River. The original bridge spans carried four lanes of vehicular traffic across the river. Because of the large increase in traffic load on this road, it was decided to add another four-lane bridge adjacent to the old structure. Although the old bridge used an electro-mechanical drive, it was decided to use a hydraulic drive system for the new bridge. While at Hamilton Engineering, Gil Lund was the Principal Engineer responsible for the conceptual design of the hydraulic drive system for the new bridge. Four hydraulic cylinders acting directly on the large trunion shaft of the bridge accomplish the bridge span lift. These cylinders are located in opposing pairs on each side of the span.