South Park Bascule Bridge Replacement

Seattle, Washington


Innovative, seismically resilient bascule bridge returns safety, mobility and spirit to Seattle community

•    Designed to withstand stringent seismic criteria
•    Incorporated historic elements of former bridge 
•    Delivered in four years

In 2008, the King County Department of Transportation selected HNTB as final design consultant to the South Park Bridge replacement project. The new bridge would restore a vital link in the South Park community of Seattle, which was suffering from the closure of the existing bridge.

HNTB designed a lift bridge to sustain minimal damage and remain operational after a 100-year seismic event and to experience only moderate, quickly repairable damage after a 1,000-year earthquake. Features included sunken caisson foundations, an isolated trunnion frame, a collapsible center joint on the lift spans and a trussed plate girder design, which emulates the character of the historically significant bridge, expedites fabrication and erection and reduces maintenance. HNTB also preserved historic elements from the original 1931 double-leaf bascule bridge and incorporated them into the new bridge and surrounding site. 

Four years after the former bridge was closed, the community can take pride in a landmark draw bridge that is safe, preserves the art and historical features of the old bridge and improves the marine and land-based environment of the surrounding areas.