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

Updated: July, 2026

What's happening now?

Construction on retrofits to help the bridge better withstand earthquakes is nearly complete! Crews have removed most of their equipment and materials from around the bridge. They will continue work on some remaining small tasks through the end of August and will return in the fall to complete landscaping.

Here’s what we’ve done to make the 15th Ave NE/NE 105th St bridge stronger and less vulnerable in the event of an earthquake:

1. Column Upgrades: We have reinforced the bridge’s columns at two locations to increase strength and resiliency against earthquake loads.
2. Crossbeam Reinforcement: The crossbeams are the horizontal pieces that connect the columns. We have added extra support to these concrete beams to improve the stability of the bridge as a whole.  
3. Foundation Work: We have made the base of the bridge stronger by adding extra support under the ground. These changes will help  steady the bridge  during an earthquake. This footing work has included:
   • Increasing the size and adding reinforcing to the concrete footings.
   • Installing piles, which are small, strong columns placed deep in the ground.
4. Water Main Upgrades: We installed a butterfly valve on the existing 30-inch water pipe, which is a round valve that helps control or stop the flow of water through the pipe.

We’ve strengthened the bridge by reinforcing its columns, crossbeams, and restoring the surrounding landscape for long-term resilience (SDOT, July 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.  

Project Area

Schedule and Construction

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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