42nd Ave Bridge S Replacement Project

Project Status Update

We are currently collecting and analyzing data to establish existing conditions to inform preliminary design options for the 42nd Ave S bridge replacement.

Crews were onsite earlier this winter conducting survey, traffic data collection, marking environmental features, and geotechnical work. The measurements and research done by surveyors informs engineers of existing site conditions and property boundaries. Crews may return to the site for follow-up investigations. This work could include clearing vegetation, additional investigations may include additional drilling, environmental, hydraulic, or surveying.

The project team recently submitted a grant for federal funding available for maintenance or replacement of existing bridges, and will be pursuing additional grants throughout the year.


Project Overview

The 42nd Ave S Bridge is an important arterial for the City of Tukwila and surrounding communities. The bridge, designed in 1927 and built in 1949, is reaching the end of its design lifespan and needs to be replaced. The current 42nd Ave S Bridge consists of a 3-span 280-foot-long bridge with a sufficiency rating of 7.56 out of 100 and is considered both Structurally Deficient and Functionally Obsolete by the Federal Highway Authority (FHWA). The 2018 average daily traffic volume (ADT) was 10,300 vehicles per day.

A consultant team has been brought onboard by the City to develop a design for a replacement bridge. A component of the design work will involve gathering feedback from community stakeholders to guide portions of the design process. There will be multiple opportunities for the public to share their thoughts on bridge design and other project features.

To stay up to date on the project and learn about upcoming feedback opportunities, please sign up for the project mailing list below.


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The project is currently in the design phase which will continue through 2021.


Type/Size/Location (TSL) Report: A TSL report will consider all reasonable replacement options eligible for federal funding and help narrow the choices down to a preferred alternative. The report will determine the functional and physical characteristics of the bridge, how it will be construction, and its location. The consultant team need community input to inform the TSL report.


Frequently Asked Questions

Why can’t the bridge be fixed instead of replaced?

The existing bridge was designed in 1927 and built in 1949 and is nearing the end of its life. The two-lane bridge has one narrow sidewalk. The existing bridge is considered both Structurally Deficient and Functionally Obsolete by the Federal Highway Administration (FHWA). Because of this, the City of Tukwila plans to replace the bridge. This bridge provides vital access to the Allentown neighborhood, Tukwila Community Center, Green River Trail, and nearby businesses.

Structurally Deficient: A structurally deficient bridge is one for which the deck (riding surface), the superstructure (supports immediately beneath the driving surface) or the substructure (foundation and supporting posts and piers) are rated in condition 4 or less (out of 9).

Functionally Obsolete: A bridge that was built to standards that are not used today. For example, they may not have adequate lane widths, shoulder widths, or vertical clearances to serve current traffic demand.


Is this project related to the BNSF Access Study?

The 42nd Ave Bridge replacement project is a separate and distinct project from the BNSF Access Study.  The 2016 BNSF alternative access study is still in draft form and a viable alternative route has not been chosen yet. The BNSF access study has been delayed because of the critical need to replace the 42nd Avenue Bridge, and the City’s civic and legal responsibility to ensure that the bridge does not fail and preserve public safety. Visit the BNSF Access Study website to learn more.


Are you looking at other locations for the new bridge?

We are looking to replace the bridge within the same traffic corridor.


When will construction on the new bridge begin?

The City has funded preliminary design at this time while grant applications are pursued.  If grant funds are able to be procured while the design is underway we anticipate having the design and right of way complete by the end of 2023.  Construction could begin in 2024 and be finalized in 2025, though it is dependent on the City’s success at receiving grant funding.


Will you have to close the bridge during construction?

This is likely, though the project would have temporary opportunities for motorists to get through. We know that construction is always challenging for neighbors and others affected by the work. Closing the bridge would make certain trips take longer, and we would look at all options that could help alleviate these effects. But the local geography that makes this bridge essential for neighborhood connectivity is also what makes detours challenging. If there is a full bridge closure, we will explore alternate routes for people walking and biking and will update you when we have more information. 30% of the traffic crossing the 42nd Ave Bridge is heavy vehicles and S 115th St is not open to large trucks. This will be a consideration when determining temporary by-pass bridge options.

Throughout design we will be working with the community and other stakeholders to assure local concerns are considered during the design phase.


What is the pre-construction timeline?

We expect to complete preliminary design and develop a recommendation for a closure and detour strategy—with neighbors’ input—by winter 2021. From there, we will conduct an environmental review and pursue permits as needed. Tukwila City Council will consider staff recommendations and the public’s input to adopt a preferred design, as well as a closure and detour strategy, by winter 2021. Design would continue through 2021, and 2022, we anticipate advertising for a construction contractor in late 2023 and beginning construction in early 2024, depending on grant availability.


Will there be detours during construction?

We expect there to be detours for vehicles, bicycles and pedestrians during construction. Once we know more about the final design of the bridge, we will be able to determine the safest alternative routes for travelers.


How long will construction take?

We anticipate that construction will take 24 months. We will have more certainty about the construction timeline after the project’s design is closer to complete and grant funding is secured.


Will construction be noisy? Will there be construction at night?

The project is in the initial design stages, which means it’s too early to say what people who live near the bridge may experience during construction. Some noise is unavoidable during construction, but the City has limits on the types of work and volume levels that can occur at night.


Will the new bridge be ADA (Americans with Disabilities Act) accessible?

The new bridge will comply with ADA requirements and provide a much more accessible experience for those crossing the bridge.


How much does this cost and where does the funding come from?

The bridge will cost approximately $21M to design and construct and the City is pursuing multiple funding sources including local, state and federal.


How will bridge construction impact the Duwamish River?

Protecting the natural environment around the bridge will be a top priority of our bridge design and construction. The bridge spans the Duwamish River, which runs directly into the Puget Sound. We will conduct an environmental review of impacts to the river, wetlands and other environmental elements in accordance with the State Environmental Policy Act (SEPA) or National Environmental Policy Act (NEPA). We will also take steps in construction to limit our impacts to the natural environment.


Project Library


Contact Information

For general project questions, please contact Adam Cox at 206-431-2446 or email