SR 520 West Approach Bridge North

This West Approach Bridge North project replaced the existing 1.2-mile long bridge structure that was seismically vulnerable to a catastrophic earthquake and extended SR 520’s three westbound lanes from the floating bridge to the Montlake area in Seattle.

1 Alliance provided design-build surveying services, including control staking and verification, curb staking, fence staking, contour staking, channelization, sawcut and barrier limits, quality assurance and quality control, office computations, and data reduction.

The project constructed a new 6,000-foot, 41 span precast girder bridge. The structure is built to modern earthquake standards and supports a six-lane corridor with a bicycle and pedestrian path, with connections to local and regional trails. Additional project benefits include environmental improvements such as a new Arboretum trail, enhanced wetlands in the Union Bay Natural Area, and a new public park along Portage Bay.

Project Details




Seattle, Washington


2016 – 2018

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