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

Updated: August 5, 2025

What's happening now?

Concrete placement work

• Crews continue making progress on column upgrades beneath the bridge. To safely complete upcoming concrete placement, the bridge will be closed on Thursday, August 7 from 9 AM to 3 PM, and again on Monday, August 11. A concrete truck will be staged on the bridge deck during this work.

Watermain work 

• We’re almost finished upgrading the water main. Now, we’re replacing sections of the roadway that were removed for this work, between NE 104th St and NE 103rd St. To do this safely, the bridge will be closed from 6 PM on Friday, August 8 to 6 AM on Monday, August 11. (Dates have been updated—the bridge closure was previously planned for August 1 to August 4.)

        Here’s the planned work schedule so you know what to expect: 

• • Friday day: Crews will begin cutting sections of the road. This work will be loud.
  • Friday night: Crews will remove the old materials of the road. This work is not expected to be as loud.
  • Saturday: They’ll prepare the area and pour new concrete.
  • Sunday: The concrete will set and harden.
  • Monday: One lane will reopen in the morning from 6 AM to 9 AM to reduce impacts to the morning commute.
    • The bridge will fully close again at 9 AM while crews finish asphalt work along the shoulder and complete concrete placement.
    • Both lanes and NE 104th St at 15th Ave NE will fully reopen in the afternoon.

Night work

• • Following the City’s standard night work requirements, crews will be working the nights of August 8, 9, and 10. 
    
    

Caption: This photo shows the crews aligning and securing a large pipe section inside a trench.

Traffic Impacts: What You Need to Know 

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.

Sidewalk and side streets impacts

• One sidewalk on 15th Ave NE at the bridge will stay open at all times.
• NE 104th St is fully closed at 15th Ave NE.
  • We’ve placed signage on NE 103rd St and NE 104th St at the intersections of 12th Ave NE and 15th Ave NE to notify people traveling.
  • This road will fully reopen on Monday, August 11. 

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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