South Park Bridge - Why the bridge closed

At the end of its useful life

After eight decades of service and the destructive effects of three major earthquakes, the South Park Bridge is at the end of its useful life. The main pier foundations are heavily cracked due to settlement and the substandard concrete in the piers is undergoing a self-destructive process that cannot be reversed or repaired. Individual portions of the piers tilt and shift in differing directions during bridge openings when the piers are most heavily loaded which causes operational difficulties. The piers have tilted toward the river so much that, even after many modifications, the bridge cannot be properly closed and the moveable parts fully seated.

Vulnerability to earthquake damage

When the South Park Bridge was designed back in the late 1920’s, earthquake design was not yet part of the bridge design code. The three earthquakes the bridge has sustained since it was built have cumulatively weakened the bridge, despite repairs completed after each earthquake. The bridge is situated on liquefiable soil and remains very vulnerable to earthquakes. The extent of these problems, coupled with the poor initial construction of the bridge, meant the bridge needed to be closed to ensure the safety of the public. The South Park Bridge was permanently closed on Wednesday, June 30, 2010 at 7 p.m.

Unreliable mechanical and electrical systems

Beyond the structural problems, the mechanical and electrical systems that open and close the South Park Bridge are unreliable. There were frequent problems that prevented the bridge from operating properly, causing significant delays for both vehicular and boat traffic. Recently over a two month period, the bridge was disabled once per week, due to electrical and mechanical problems, disrupting both vehicular and marine traffic.

Second opinion confirms King County's findings

King County commissioned an independent study of the South Park Bridge's condition to confirm our assessment of the bridge and our decision to close it on June 30. The results of this study confirmed our own findings and our schedule for closing the bridge.

Information on the South Park Bridge website is available to people with disabilities in alternate formats upon request by calling 206-263-6482 or 711 for the TTY relay service.

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