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King County Road Services - Capital Improvement Program

South Park Bridge #3179 - Replacement Project

Project No.:  1026739
Project limits:  14th/16th Ave S. over Duwamish River
Project type:  Bridge
Thomas Bros. Map No.:  625b3

Project description

Construct a new moveable bridge over Duwamish Waterway parallel to and downriver of the existing bridge. The bridge replacement project will also realign the intersection of 14th Avenue South and Dallas Avenue South/South Sullivan Street, construct natural water treatment systems such as a rain garden, build roadway and drainage facilities, relocate conflicting utilities, restore riverbanks by creating gentle slopes for tidally influenced areas and planting riparian vegetation.

Why is King County doing this project?

The existing bridge was built in 1929-1931 and closed on June 30, 2010 due to its severe deterioration and vulnerability to earthquakes. The original foundation piles were not driven deep enough, making the bridge susceptible to settlement and resulting in the tilting and cracking of the main piers. The mechanical and electrical systems that operated the bridge were unreliable and required repairs frequently. With lanes narrower than standard, the bridge carried up to 20,000 vehicles daily with 14% being truck traffic.

Project management phase:  Construction 95%

Status as of December 17, 2014

Bridge opened to traffic on September 2 for all lanes of traffic; one in each direction, a bike lane, and sidewalks. Final construction activities will include: rain garden platform installation, painting, interpretive sign installation, minor control tower finishes, and final punchlist.

Environmental information

The South Park Bridge spans the navigable channel of the Duwamish Waterway, which is used for industrial, commercial, and recreational purposes. The natural habitat in the project area has been extensively altered through human activity. Urban landscapes in the form of landscaped backyards, parks, street trees, and undeveloped steep slopes are the primary terrestrial habitats in the vicinity of the project area. To reduce environmental impacts during project construction, certain in-water work must be completed during a 6 1/2 month work window between August 1 and February 15th annually. Some of this work involves removing about 352 creosote-treated piles that serve as pier protection for the existing bridge. They will be removed/cut off and replaced with steel piles, thus improving water quality. Removal of the existing approach bridge piers will remove 671 square feet of structure from intertidal areas of the Duwamish River used by migrating salmonids. The project-wide mitigation plan will include shoreline enhancement, including removal of bank armoring, creation of new intertidal zone, and riparian planting, which will partially offset affected functions and values within the Duwamish Basin, and water quality treatment for impervious surfaces.

See also

Environmental compliance for bridge activities External link graphic
King County Annual Bridge Report
Overlegal truck permit
Road closures
Road standards
Roads' future - learn what's needed to preserve our road network
Seattle bridges External link graphic
Title VI information
WSDOT Historic Bridges External link graphic

How does the CIP work?

The Road Services Division Capital Improvement Program (CIP) contains all design and construction and studies for improvements on roads, bridges or transportation facilities in the unincorporated areas of King County. We have a glossary to help explain our terms and jargon.

Budget and Funding

Vicinity map

Vacinity map

Project supervisor

Jim Markus