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

Updated: December, 2025

What's happening now?

Upcoming Concrete Work 

• Crews will be pouring concrete on the shoring walls, which are temporary support walls for the bridge during construction. This work is part of the ongoing effort to make the bridge better withstand earthquakes. To get this done, concrete trucks will be parked on the bridge and crews will be moving materials around the work area.

How Will This Work Impact You?  

• From the beginning of December through the middle of the month, the southbound lane at the bridge will be closed from 9 a.m. to 3 p.m. to make space for the concrete trucks. 
• A flagger will be on site during the day to direct traffic, alternating people driving across the bridge. 
• At the end of each workday, crews will reopen the southbound lane. 
• Crews will fully close the bridge on December 8 and December 9 from 9 a.m. to 3 p.m. to move materials. 
• These closures won’t block driveways on 15th Ave NE between NE 104th St and NE 105th St.  
• People walking or using mobility devices can still use the bridge during full closures. 

Year-End Progress Update 

• Water main upgrade: Earlier this year, crews upgraded the water main in the project area. This upgrade added an additional valve and installed a vault, which created another point where Seattle Public Utilities can turn off this water main when needed. 
• Crossbeam retrofits: Crews have been working on retrofits to the bridge’s crossbeams for most of this year. Crossbeams are horizontal supports that connect to the vertical parts of the bridge, adding stability and strength. 
• Footing retrofit: This fall, crews began work on another seismic retrofit, micro piling, which involves installing long, slender columns called piles into the ground at the base of the bridge. These retrofits to the bridge footing will improve stability and the bridge's ability to better withstand seismic events. Crews installed test piles and conducted testing this year to prepare to install permanent piles. 

Caption: In the upper-left photo, crews use a construction vehicle to move a timber pier as part of retrofits to the bridge’s footing. In the upper-right photo, a crew member taps into the water main to add a valve and install a new vault. In the lower-left photo, crews use a lift to place a supporting beam under the bridge as part of seismic retrofits. And in the lower-right photo, workers test a newly installed pile to ensure it meets safety requirements. Together, these activities support the ongoing effort to strengthen the bridge so it can better withstand earthquakes.

Here’s what you can expect in 2026: 

• Crossbeam retrofits: Crews have approximately 3 crossbeams left to retrofit. They’ll continue to place reinforcing bars, create concrete forms, and pour concrete crossbeams between the bridge columns during full closures as they make progress on these retrofits. This work will continue through spring 2026. 
• Footing retrofit: Now that preliminary testing is complete, crews are installing permanent piles as part of retrofits to the bridge footing. They’ll be installing these piles through early 2026. 
• Landscaping: Once crews complete retrofits to the bridge’s crossbeams and footing, they’ll landscape the area under the bridge. We expect this work will happen in spring 2026. 

We expect the project to be finished in summer 2026. 

If you have questions about this project, please contact us at BridgeSeismicRetrofit@seattle.gov or (206) 775-8734. To receive project updates, sign up to join our project listserv. 

About the Project 

Seattle is located in an earthquake-prone region, and earthquakes can seriously impact our bridges. To address this risk, the City of Seattle created the Bridge Seismic Program to evaluate which bridges are vulnerable and reinforce them to better withstand seismic events.    

As part of the Levy to Move Seattle, 16 bridges were selected for seismic reinforcements, including the 15th Ave NE and NE 105th St bridge. This bridge is a 480-foot-long concrete bridge designed by Homer Hadley and constructed in 1949, prior to the modernization of the seismic design code. 

Spanning a forested ravine over Thornton Creek and connecting to Northgate Way area, the 15th Ave NE and NE 105th St bridge 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. 

Here’s what we’ll do to make the bridge stronger and less vulnerable in the event of an earthquake:

• Foundation Work: We will make the base of the bridge stronger by adding extra support under the ground. We will reinforce the concrete footings and install micropile foundations, which are small, strong columns placed deep in the ground. These changes will help the bridge stay steady and safe during earthquakes.
• Column Upgrades: We will reinforce the columns at two locations to increase strength and resiliency against earthquake loads.
• Crossbeams Reinforcement: The crossbeams are the horizontal pieces that connect the columns. We will add extra support to these concrete beams to improve the stability of the bridge as a whole.

Additionally, this project includes: 

• Water Main Upgrades: 
  • We will be working on an existing water pipe that is 30 inches wide.
  • We are also adding a butterfly valve, which is a round valve that helps control or stop the flow of water through the pipe.
     

  Project Area

Schedule and Construction

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.

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