15th Ave NE & NE 105th St Bridge Seismic Retrofit
Updated: June, 2025
What's happening now?
Crews have started excavation work for the water main upgrades and will continue making progress over the next few weeks.
As part of this work, a temporary closure of NE 104th St at 15th Ave NE will be in place starting June 2 and is expected to last for approximately four weeks.
Caption: Crews excavation work for the water main upgrade near NE 104th St and 15th Ave NE.
Traffic Impacts Reminder: Work In Progress
Traffic impacts on 15th Ave NE at the bridge
- Ongoing one-lane closures started in April.
- 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 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.
Photo Caption: Crews have started working on and 15th Ave NE/NE 105th St bridge retrofits. Temporary traffic control measures are now in place. Please, follow signs and drive slowly in active construction zones.
We expect the project to be finished in summer 2026.
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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
| Planning | October 2018-April 2020 |
| Design | January 2021-December 2022 |
| Potholing Work | Late November - December 2024 |
| Construction Began | January 2025-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.
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