15th Ave NE & NE 105th St Bridge Seismic Retrofit

Updated: May, 2025

What's happening now?

We’re preparing the site for construction on the 15th Ave/105th St Bridge. This work includes placing a temporary work bridge over Thornton Creek and installing temporary decking. Once site preparation is complete, we’ll start reinforcing the bridge's crossbeams.

We expect the project to be finished in summer 2026.

How Will This Work Impact You?

Traffic impacts on 15th Ave NE at the bridge

Ongoing lane reductions will start as early as April 14.
Most of the time, one lane will stay open. Crews will use flaggers or temporary signals to direct traffic.
During this work, on-street parking won’t be available.
Crews will occasionally close both lanes on the bridge (full closure). We’ll share advance notice and alternate routes when that happens.
- These closures won’t block driveways on 15th Ave NE between NE 104th St and NE 105th St.
- People walking or using mobility devices will still be able to use the bridge during full closures.

Sidewalk and side streets impacts

One sidewalk on 15th Ave NE at the bridge will stay open at all times.
At times, we’ll need to fully close NE 104th St at 15th Ave NE.
We’ll post detour signs and send advance notice when that happens.

Excavator working under a bridge near a forested slope, with workers and erosion control barriers nearby.

Photo Caption: Crews worked on site preparation earlier this year under the bridge, including clearing vegetation and grading access paths.

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Project overview

Earthquakes could have a detrimental effect on Seattle's infrastructure. To address seismic risks to city infrastructure, the City of Seattle established a bridge seismic retrofit program to assess the seismic vulnerability of the City's bridges and to prioritize limited funding to reduce this transportation infrastructure vulnerability.

As part of the Levy to Move Seattle, 16 bridges were selected for seismic retrofits, including the bridge at 15th Ave NE and NE 105th St. The 15th Ave NE Bridge is a 480 feet long concrete bridge designed by Homer Hadley and constructed in 1949 using innovative techniques, but prior to the modernization of the seismic design code. Spanning a forested ravine over Thornton Creek and connecting to Northgate Way area, it carries both vehicular and pedestrian traffic and is supported by five concrete piers. SDOT strengthened the original concrete box girders, added new abutments, and made other improvements to the bridge in 2011.

The planned seismic retrofits to the 15th Ave NE Bridge build on the previous strengthening and include several modifications to seismically strengthen existing bridge piers and reduce the bridge's vulnerability to earthquakes.

Graphic showing cross section of bridge structure and where our proposed work is located.

What to expect during construction

Access to homes will stay open. If we need to block a driveway, we’ll notify you ahead of time.
Crews will work in public areas near homes and businesses.
Expect typical construction impacts like noise, dust, vibrations, and equipment on site.
Work hours are 7 AM to 5 PM, Monday through Friday.

Project Area

Schedule and Construction

Planning	October 2018-April 2020
Design	January 2021-December 2022
Potholing Work	Late November - December 2024
Construction Began	January 2025

We expect the project to be finished in summer 2026.

Construction schedules are also subject to change and depend on factors such as weather and availability of crews and materials.

Funding

The total project estimate is $6 million and is currently funded through the Levy to Move Seattle. Approved by voters in 2015, the 9-year, $930 million Levy to Move Seattle provides funding to improve safety for all travelers, maintain our streets and bridges, and invest in reliable, affordable travel options for a growing city.

Translation and interpretation

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