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

Updated: September 3, 2025

What's happening now?

Upcoming Bridge Closure

• Crews will close the 15th Ave NE/NE 105th St bridge from 9 a.m. to 3 p.m. on Thursday, September 11 to pour concrete crossbeams as they continue work on the bridge to make it better withstand earthquakes. These crossbeams are horizontal supports that connect to the vertical parts of the bridge, adding stability and strength.
  • Driveways on 15th Ave NE between NE 104th St and NE 105th St will remain accessible.
  • People walking or using mobility devices can still cross the bridge during full closures. 

Progress Update

• Crossbeam retrofits: In the past few weeks, crews have worked on the mid crossbeam and upper crossbeam retrofits.  They have completed about a third of the crossbeam retrofits and will continue working on them for the next month. 
• Water main update: The water main upgrades are now complete.

Caption: Construction crews smooth concrete on a new section of the roadway, which was replaced after water main upgrades were completed [left]. Construction crews place reinforcing bars in preparation for the concrete pour that will add resiliency to the bridge’s crossbeams during a seismic event [right].

Traffic Impacts: What You Need to Know 

Sidewalk impacts

• One sidewalk on 15th Ave NE at the bridge will stay open at all times.

Lane closures on 15th Ave NE at the bridge

• Ongoing one-lane closures 
  • Usually, one lane will stay open, with flaggers or temporary signals guiding traffic.
• On-street parking won’t be available throughout the project.
• Crews will fully close the bridge at least once a week. 
  • 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

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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