SR 520 advisories
For the most up-to-date information about SR 520 construction activities and planned road closures, visit and bookmark our SR 520 Construction Corner and its interactive construction map. Read the latest SR 520 news in our weekly email update. You can also view Montlake Project construction photos taken 'round the clock by our four mounted construction cameras.
Plans and process
The SR 520 Bridge Replacement and HOV Program is rebuilding one of the Puget Sound region's busiest highway corridors. We’re replacing vulnerable bridges, improving traffic safety, enhancing regional mobility and providing new and better options for nonmotorized travel. To keep traffic flowing during reconstruction, we are rebuilding SR 520 in stages – mainly from east to west. You’ll find more information about the phased work on our Related Projects tab.
Public engagement plays an important role in the planning and project designs of SR 520’s reconstruction. You will find key SR 520 design reports on our Community Engagement tab.
End result
Here’s what the public will see when the SR 520 corridor’s reconstruction is complete:
- New, structurally resilient bridges over Lake Washington, Union Bay and Portage Bay.
- A dedicated bus/carpool lane in each direction between Seattle and Bellevue.
- Three transit stations for local and regional bus routes.
- Five landscaped freeway lids over SR 520 – three on the Eastside, two in Seattle.
- A 14-foot-wide walking and cycling trail between Seattle and Bellevue, a bicycle-pedestrian “land bridge” over SR 520 in Seattle’s Montlake neighborhood and a 30-foot-wide bicycle and pedestrian crossing over I-5.
- A reversible transit/HOV lane along I-5’s express lanes between the SR 520 and Mercer Street interchanges, with reversible ramps at both interchanges.
- A system to capture and filter out stormwater pollutants from SR 520 highway runoff.
Benefits of this program
Improves safety
- The new floating bridge, designed to withstand a 100-year storm, is supported and stabilized by more than twice as many pontoons (77 vs. 33), with heavier anchors and stronger anchor cables. The old SR 520 floating bridge outlived its design life and risked failure in a severe windstorm.
- The new bridges over Union Bay and Portage Bay will be built to current seismic standards, able to withstand a once-in-a-1,000-year earthquake. The old bridges, supported by hollow columns, are vulnerable to collapse in a severe earthquake.
- The new floating bridge’s roadway deck sits higher above the water than the old bridge’s roadway. This allows WSDOT crews to perform important maintenance and safety work from the pontoon deck beneath the roadway.
- Direct-access ramps at 108th Avenue Northeast allow safer and easier highway access for buses and carpoolers. The transit hub on a new Montlake freeway lid over SR 520 also will have direct-access ramps to and from the highway.
- The highway’s transit/HOV lanes are located along the median, eliminating conflicts between buses and vehicles merging onto or off SR 520's general-purpose lanes.
- The ADA-compliant transit stations are separated from highway traffic, providing safer access for bus riders.
- The rebuilt highway’s new interchanges have longer on- and off-ramps with improved sight lines for drivers.
Relieves congestion
- The old corridor has only two general-purpose lanes in each direction, with no HOV lanes. The rebuilt corridor features two general-purpose lanes and one bus/carpool lane in each direction.
- The old highway has no shoulders for disabled vehicles. The rebuilt corridor has full shoulders, which eliminate lengthy backups and traffic safety hazards from disabled vehicles stuck in a travel lane.
- Travel time from Seattle to Bellevue in the HOV system, when completed, should decrease by up to 25 minutes during peak periods. Drivers in the general-purpose lanes should save about a half hour. Those time savings compare to travel time under a no-build scenario with no improvements to SR 520.
- A study of the rebuilt Eastside segment of SR 520 found that drivers should save 1.4 million hours of travel time and $467 million in travel-time savings every year.
Provides multimodal options
- The 14-foot-wide SR 520 bicycle and pedestrian trail provides a new cross-lake connection for both commuting and recreating, with connections to local trail networks. When SR 520 construction is complete, the SR 520 Trail will extend from Seattle to Redmond.
- The addition of transit/HOV lanes and the cross-lake shared-use trail provide more travel options and greater reliability to accommodate growth in the region.
- A new, reversible transit/HOV lane will connect SR 520 and Seattle’s I-5 / Mercer Street interchange. Bus and carpool riders will have more reliable trips between the Eastside and Seattle’s South Lake Union and downtown neighborhoods
- The SR 520 Program helped develop the Montlake Multimodal Center, a key regional transit hub next to Husky Stadium. This hub provides connections to local and regional buses, regional bicycle and pedestrian trails and the University Link light rail station.
- The new floating bridge is designed to accommodate the addition of light rail – with a retrofit – if voters choose to fund that option in the future.
Enhances the environment
- The rebuilt highway and its fixed-column bridges will capture and carry roadway runoff to on-land stormwater retention and treatment sites. These sites filter out pollutants and improve water quality in the Lake Washington watershed. Also, the new floating bridge captures runoff and screens out polluting sediments before the runoff flows into the lake.
- The improved highway reduces carbon emissions by enhancing transit use and nonmotorized travel.
- The SR 520 Program supports several major enhancement projects in the Washington Park Arboretum. One effort is to remove old ramps that ran through the park. These include the old SR 520 on- and off-ramps and never-used R.H. Thomson "Ramps to Nowhere."
- Additional SR 520 environmental projects are enhancing parks, streams, wetlands and other natural areas across the region to mitigate for the effects of project construction.
- The SR 520 Program installed eight large, fish-friendly culverts on the Eastside to aid fish migration.
Visit our Environment tab to learn more about the program's environmental initiatives.
Promotes a smarter design
WSDOT employs a planning process called "practical design" that engages the community early on to help us make project decisions that produce cost-effective, sustainable results. On the SR 520 Program, practical design has reduced costs and improved results in the following ways:
- A modified design for the West Approach Bridge North reduced the number of in-water columns by 40 percent, which saved money and shrank the bridge’s environmental footprint.
- Smarter highway technology on the new floating bridge – variable speed-limit signs and reader-board displays with real-time traffic information – boosts traffic efficiency and helps drivers make safer, smarter decisions.
- A smarter design for the Montlake lid retains desirable public space and improves transit, bicycle and pedestrian accessibility while removing costly ventilation and maintenance systems.
- A reduced, 45 mph speed limit on a new Portage Bay Bridge will lower the noise caused by tires on bridge pavement and lessen noise in surrounding neighborhoods.
Building a new and improved SR 520 corridor
Every day tens of thousands of people travel on SR 520 to reach offices, schools, industries, entertainment venues and more. The SR 520 Bridge Replacement and HOV Program is enhancing public safety and mobility by replacing this vital urban highway’s aging and vulnerable bridges. The program also is making major transit, roadway and trail improvements throughout the corridor, along with significant environmental enhancements throughout the region to mitigate for project effects.
This effort involves reconstructing a six-mile stretch of the corridor between I-5 in Seattle and I-405 in Bellevue. SR 520 construction, which began in 2011, is occurring in separate, phased projects. The corridor’s final improvements in Seattle are scheduled for completion in 2029.
Public engagement shapes corridor’s improvements
Years of public engagement, planning, design and engineering work preceded the start of SR 520’s reconstruction. Public feedback has played a critical role in shaping the scope and design of the highway’s improvements. This began in the late 1990s with the Trans-Lake Washington Study. It continued through the environmental impact studies in the 2000s and is part of the design refinements still occurring today.
You will find key SR 520 planning and design reports on our Community Engagement tab.
Budget and funding
The total funding of the SR 520 corridor is $5.69 billion.
The corridor’s improvements are funded by local, state, and federal dollars:
- Federal funding (Grant Anticipation Revenue Vehicle and others): $1.12 billion
- Federal loan (The Transportation Infrastructure Finance and Innovation Act): $0.30 billion
- State funding (Others*): $0.69 billion
- State funding (Connecting Washington account): $2.06 billion
- State funding (SR 520 Corridor account): $1.20 billion
- State funding (deferred sales tax): $0.30 billion
- Local funding: $0.02 billion
*Includes Transportation Partnership Account, SR 520 Civil Penalties Account, Motor Vehicle Account, and JUDY Transportation Future Funding Program Account.
Tolling the SR 520 floating bridge
Tolling on the old SR 520 bridge across Lake Washington began when the bridge opened in 1963. The tolls continued until the construction bonds were paid off in 1979. Tolling restarted on the old bridge in late 2011 to help pay for the new floating bridge.
Tolling on the new bridge began when it opened in spring 2016. The tolls help pay off construction bonds and cover bridge operations, maintenance, insurance and deferred sales tax. SR 520 tolling is projected to generate approximately $1.2 billion. You’ll find more information about tolls on WSDOT’s Good To Go! website.
SR 520 history
The communities along the SR 520 corridor between I-5 and the Eastside boast a rich cultural heritage within a diverse and abundant natural setting. From waterways to highways and canoes to trains, this area has been home to ever-changing communities, neighborhoods, industries and innovations.
520history.org is dedicated to the history of the communities, industries, and landscapes that have developed throughout the SR 520 corridor. Check out the website for an in-depth look at 13,000 years of history, from early tribes to bustling communities on both sides of Lake Washington. You’ll learn about early settlements, major changes to the natural landscape, and transportation infrastructure and bridge construction that facilitated population and employment growth.
Upcoming public engagement opportunities
Monthly Montlake Project construction update meeting
Our next Montlake Project monthly meeting will be held online at 12:30 p.m. Wednesday, Oct. 16. Learn more and register. Missed our last monthly meeting? You can view the presentation online (PDF 10MB) or view the meeting recording on YouTube.
We’ve recently heard concerns from Montlake neighbors about signage and are continuing to work with the to community to address these concerns. For past meeting materials, see the Montlake Project webpage under the "Related links" tab.
Diversity and inclusive contracting
WSDOT is committed to seeing that all Washingtonians have access to the thousands of family-wage jobs generated by our projects. We establish goals for each project to promote participation and inclusion of small, disadvantaged business enterprises owned by minorities, veterans or women. Our Key Projects tab contains information about our ongoing opportunities for small and diverse firms with the SR 520 Program. Visit the WSDOT Office of Equity and Civil Rights website for more information and resources about working with WSDOT.
Commitment to diversity and inclusive contracting – WSDOT goals for state-funded projects
On projects supported entirely with state funds, WSDOT set a voluntary goal of 26 percent participation by minority-, small, veteran- and women-owned business enterprises (MSVWBEs). This goal is broken down into goals of 10% participation by minority-owned business enterprises, 6% participation by women-owned business enterprises, 5% participation by veteran-owned businesses, and 5% participation by small business enterprises. Please read WSDOT's Diversity Roadmap (PDF 284KB) for additional information on WSDOT's inclusive contracting goals. The current SR 520 Montlake Project and future SR 520 “Rest of the West" (PDF 3.3MB) projects in Seattle are fully state-funded projects.
We participated in a contractor forum in February 2022 about contracting opportunities on two WSDOT megaprograms, including the SR 520 Program’s upcoming Portage Bay Bridge and Roanoke Lid Project. You can learn more by viewing the forum presentation (PDF 2.6MB).
Quarterly progress reports
You can read the latest Diversity and Inclusion quarterly progress report (PDF 1.6MB) covering all WSDOT Megaprograms for Q2 2024. See page 5 for the SR 520 Program. You can also read these past WSDOT Megaprogram reports:
Tips and Tools
WSDOT periodically publishes "Tips and Tools" to provide small businesses owned by minorities, women or veterans with useful information on potential contract opportunities with WSDOT and other government agencies.
Questions or comments about contract opportunities on WSDOT projects?
Regina Glenn (she/her)
Diversity and Inclusion Manager, WSDOT Megaprograms
Phone: 425-295-4626
Cell: 425-503-7212
Email: GlennRe@consultant.wsdot.wa.gov
Community Liaison & Ombudsman
David Goldberg serves as the community liaison and ombudsman for the SR 520 Bridge Replacement and HOV Program. It’s his role to represent and advocate the interests and concerns of the communities we serve. He’s here to listen and understand how the reconstruction of the SR 520 corridor affects community members. This includes nearby residents, users of the transportation system, community-based organizations, elected representatives and other affected stakeholders. David strives to help WSDOT leadership anticipate potential issues and avoid unnecessary impacts. When community members raise issues, he investigates and seeks to work out a resolution. Learn more about David and his role in this video.
Have a question or concern about SR 520 construction?
David Goldberg (he/him)
Community Liaison & Ombudsman
Phone: 202-412-7930
Email: David.Goldberg@wsdot.wa.gov
Address:
WSDOT
999 3rd Ave., Suite 2200
Seattle, WA 98104
History of SR 520 design development through community engagement
WSDOT has been working for many years with agency partners, stakeholders and the public to develop the design of the SR 520 Program. Major steps in this process are described below. You can view some of the relevant environmental documents noted below on our Environment tab.
- 2006: WSDOT publishes the Draft Environmental Impact Statement (EIS) for the SR 520 Program’s plans between I-5 in Seattle and Medina. This builds on previous studies of options to replace the aging, seismically vulnerable SR 520 bridge across Lake Washington. WSDOT decides to continue evaluating only no-build and six-lane alternative design options. This is based on analysis in the Draft EIS and public feedback.
- 2007-2008: In response to legislative direction, WSDOT organizes a stakeholder mediation process with elected officials, local, federal and state agencies, neighborhood representatives and local organizations. The process resulted in three six-lane design options.
- 2009: WSDOT publishes the Eastside Consolidated Urban Design Report for the SR 520 Eastside Transit and HOV Project. This report summarizes the development of architectural concepts and design refinements for the project, based on community involvement.
- 2010: WSDOT publishes the supplemental draft EIS that recommends a six-lane preferred design alternative. The state Legislature directs WSDOT, the Seattle mayor and the Seattle City Council to establish a workgroup of agency partners. These partners include King County Metro, the University of Washington, Sound Transit and the Arboretum and Botanical Garden Committee. The workgroup coordinates with the Seattle Design Commission and the Seattle pedestrian and bicycle advisory boards. Together, they provide recommendations on the preferred design alternative.
- 2010: WSDOT publishes the final EIS for the Pontoon Construction Project in Aberdeen, Washington, where the largest pontoons for the new SR 520 floating bridge would later be built.
- 2010: WSDOT completes and publishes the Environmental Assessment for the Eastside Transit and HOV Project.
- 2011: WSDOT publishes the final EIS, analyzing the preferred alternative design and incorporating the design refinements from the 2010 workgroup. The Federal Highway Administration issues a Record of Decision approving the final EIS and the preferred alternative as the project’s preliminary concept design.
- 2011-2012: WSDOT works with Seattle officials, design professionals and the public to refine the conceptual design for SR 520 in Seattle. This process includes seven public workshops, thousands of public comments, and extensive coordination with the public and key partner agencies. After this, WSDOT publishes a Seattle Community Design Process final report (PDF 31MB). This report summarizes design refinements incorporated into the SR 520 conceptual design.
- 2014-2015: Following a legislative directive, WSDOT continues working with the city of Seattle and design professionals. Together, they recommend further analysis of elements that weren’t resolved in the 2012 process. This leads to several design refinements, such as a recommended bridge type for the Portage Bay Bridge. Another refinement is the addition of a bicycle and walking path on the future Portage Bay Bridge. This is part of a plan for more bicycle and pedestrian connections to existing and planned city networks. They also recommend improved open space on the Montlake lid.
- 2016: WSDOT and the city of Seattle finalize a West Side Design Refinements final report (PDF 61.9MB). This summarizes the 2014-2015 outreach and analysis and contains the final concept design for the SR 520 elements in Seattle. WSDOT also worked with city of Seattle agencies and the Seattle Design Commission. This collaboration refined the conceptual design of the Montlake Project elements.
- 2019: Through a six-month outreach process, WSDOT gets public feedback on the Portage Bay Bridge and Roanoke Lid Project’s conceptual design. The outreach included open houses, three design workshops and coordination with the city of Seattle and Seattle Design Commission. A Community and Stakeholder Outreach report (PDF 4.2MB) summarizes the outreach and the public’s design ideas for key project elements. The report includes how WSDOT incorporated those ideas into a refined design concept and the verbatim comments from the community.
Ongoing projects
The SR 520 Montlake Project replaces the old, structurally vulnerable eastbound bridge over Union Bay and adds a dedicated HOV/transit lane. This project also builds a three-acre, landscaped lid over the highway in Montlake and, east of the lid, a bicycle and pedestrian land bridge over the freeway. Learn more about this work on the Montlake Project webpage.
The SR 520/I-5 Express Lanes Connection Project creates a dedicated, reversible transit/HOV connection between SR 520 and Seattle’s I-5/Mercer Street interchange. Learn more about this work on the SR 520/I-5 Express Lanes Connection Project webpage.
The SR 520 Portage Bay Bridge and Roanoke Lid Project will build a new Portage Bay Bridge and construct a landscaped freeway lid over the highway in Seattle’s Roanoke neighborhood. Learn more about this work on the Portage Bay Bridge and Roanoke Lid Project webpage.
Upcoming projects
The SR 520 Montlake Cut Bascule Bridge Project will construct a second moveable bridge over the Montlake Cut. WSDOT will conduct additional coordination with community stakeholders and agency partners regarding the scope and timing of this project.
Completed Projects
The SR 520 West Approach Bridge North Project constructed a new, three-lane bridge across Union Bay for westbound traffic between the floating bridge and Seattle’s Montlake neighborhood. Learn more on the West Approach Bridge North Project webpage.
The SR 520 Floating Bridge and Landings Project replaced the world’s longest floating bridge with an even longer, safer bridge that includes a new, separated path for bicyclists and pedestrians. Learn more on the Floating Bridge and Landings Project webpage.
The SR 520 Eastside Transit and HOV Project rebuilt a 2.3-mile stretch of SR 520 between I-405 and Lake Washington. The project added a dedicated HOV/transit lane, three landscaped freeway lids and two median transit stops. Learn more on the Eastside Transit and HOV Project webpage.
The SR 520 Pontoon Construction Project built 33 of the new floating bridge’s 77 pontoons in Aberdeen, Washington. We built the other 44 pontoons in Tacoma, Washington. Learn more on the Pontoon Construction Project webpage.
We extensively document the history and progress of SR 520 construction through photo and videos. See below for project maps and various photo and video collections, including archived construction camera footage, that tell the story of the corridor’s reconstruction.
SR 520 Bridge Replacement and HOV Program
Photos and videos covering the SR 520 Program’s design, project highlights, public meetings and more.
SR 520 Montlake Project
Photos, videos and live construction cameras covering the work to replace the aging eastbound SR 520 bridge over Union Bay. Also covers work to construct a new landscaped lid and transit hub over the highway in Seattle’s Montlake neighborhood.
SR 520/I-5 Express Lanes Connection Project
Map and videos of the SR 520/I-5 Express Lanes Connection Project, which will create a dedicated, reversible transit/HOV connection between SR 520 and Seattle’s I-5/Mercer Street interchange.
SR 520 Portage Bay Bridge and Roanoke Lid Project
Map of the SR 520 Portage Bay Bridge and Roanoke Lid Project, which will rebuild the Portage Bay Bridge and construct a landscaped freeway lid in Seattle’s Roanoke neighborhood. Photos and video for this project will be posted once construction is underway.
SR 520 Montlake Cut Bascule Bridge Project
Map of the SR 520 Montlake Cut Bascule Bridge Project, which will construct a second moveable bridge over the Montlake Cut. WSDOT will conduct additional coordination with community stakeholders and agency partners regarding the scope and timing of this project. Photos and video for this project will be posted once construction is underway.
SR 520 West Approach Bridge North Project
Photos and videos covering the work to build a new westbound bridge between the new SR 520 floating bridge and Seattle’s Montlake neighborhood. These collections include construction time-lapses, project tours and informational videos about project features.
SR 520 Floating Bridge and Landings Project
Photos, videos and archived construction camera footage of crews building the world’s longest floating bridge. These collections include project updates, construction time-lapses and a documentary of planning and building processes.
SR 520 Pontoon Construction Project
Photos, videos and archived construction camera footage of the pontoon construction effort in Tacoma and Aberdeen, Washington. Includes time-lapse videos of the pontoons as they are floated out into the water to be transported by tugboat to Lake Washington.
SR 520 Eastside Transit and HOV Project
Photos and videos covering the expansion of the SR 520 corridor on the Eastside, from Medina to I-405. Includes time-lapse videos of construction work during highway closures.
Environmental news
WSDOT recently published a memorandum regarding the design of the replacement for the Boyer Steps as part of the Portage Bay Bridge and Roanoke Lid Project. You can read the Boyer Steps memorandum (PDF 3MB) online.
Throughout our reconstruction of the SR 520 corridor, we’ll produce environmental documents and post them when they’re available. Scroll to the bottom of this page to see our library of environmental documents relevant to current and future SR 520 project work.
Environmental Overview
WSDOT is committed to building and maintaining a sustainable, multimodal transportation system – one that supports healthy communities and the local economy while protecting the environment. We plan, design and construct our projects with the goal of limiting their environmental effects or avoiding them altogether. When project effects are unavoidable, we collaborate on initiatives to reduce them.
For the SR 520 Program, we integrate environmental considerations into our planning and design phases to reduce the environmental effect of the rebuilt corridor. During construction, we employ environmentally friendly practices to reduce our ecological footprint. We also work with communities to mitigate the environmental effects of our construction program, in part by making significant improvement to local parks and sensitive natural areas.
Building an environmentally smart highway
One way we support the environment is by making up-front decisions in the planning and design phases of our highway program. Smart planning ensures that we reduce our environmental effects and, where possible, improve our natural surroundings. Examples include:
- Low-impact structural designs that reduce steel and concrete requirements. The West Approach Bridge North design reduced by 40% the number of in-water columns and the amount of concrete needed to build them. On the floating bridge project, our design strategies reduced rebar use by 260 tons, steel use by 1,600 tons and concrete use by 12,500 cubic yards.
- Dedicated transit/HOV lanes and median transit stops between Seattle and Bellevue. These allow the highway to carry up to 17% more people during peak traffic and 5% to 10% more vehicles.
- A cross-lake bicycle and pedestrian path that provides better connections to bus and light-rail stops and local bike paths. In the future, the path will also connect to a new freeway lid and transit hub in Seattle's Montlake neighborhood.
- A projected 10% reduction in greenhouse gas emissions within the corridor when compared to a no-build option thanks to improved traffic movement and increased transit ridership.
- New stormwater management systems along the corridor, including on the new floating bridge, to capture and treat highway runoff and improve water quality in local streams and Lake Washington.
- Noise-reduction measures, including quieter concrete pavement, noise-absorbing materials at lid portals, taller traffic barriers and noise walls on the Eastside.
- Highway lids that reconnect neighborhoods, provide better transit connections and increase community green space.
- A floating bridge design that could be retrofitted for light rail if the region chooses that option in the future.
A bicyclist rides across Lake Washington on the SR 520 Trail.
Sustainable construction practices
Reducing our ecological footprint during construction is another way we strive to be environmental stewards. Examples include:
- Requiring our SR 520 contractors to develop and implement ecologically sustainable construction practices. These include reducing, reusing and recycling construction materials. On the floating bridge project, for example, the contractor sold the old bridge’s concrete pontoons to a third party. They can now be used in other regions as wharfs, piers or other marine structures.
- Reclaiming or using existing industrial sites for construction of SR 520 bridge components or corridor infrastructure.
- Using specialized “bubble curtains” in Lake Washington to reduce underwater construction noise from pile driving, which can harm fish.
- Using truck-wash stations in construction areas to reduce dust and keep streets and highways cleaner as our construction vehicles come and go.
- Placing silt and turbidity curtains around construction areas to halt erosion, prevent runoff and contain dredged sediments.
- Using vegetable-based hydraulic fluids in construction equipment to minimize environmental damage if a spill occurs.
Crews on the Montlake Project employ bubble curtains to reduce
underwater noise from construction of the new eastbound bridge.
Enhancing parks and natural areas
Within the densely populated SR 520 corridor, we are mitigating our work’s effects by restoring wetlands, improving creeks and ponds, building and enhancing trails, rehabilitating shorelines and restoring fish-migration corridors. We’ve already completed most of these mitigation projects, while a few final projects will be completed nearer to the conclusion of the SR 520 program.
A jogger uses a new loop trail WSDOT helped fund in the Washington Park Arboretum.
Park enhancements
Improvements to the Washington Park Arboretum, including:
- A new multiuse trail that serves as an important bicycle and pedestrian link from East Madison Street to Montlake and the University District.
- An enhanced pedestrian crossing under SR 520 on Foster Island.
- Funding to help with completed and future repairs and maintenance of the park’s Waterfront Trail.
- Removal of SR 520 on- and off-ramps in the Arboretum and the never-completed R.H. Thomson Expressway “Ramps to Nowhere.” This will reduce vehicle traffic through the Arboretum and create a more open and natural park area.
Funding the development of the Fritz Hedges Waterway Park, a new 4-acre public park along Portage Bay near the University of Washington. The Seattle park opened to the public in fall 2020.
Corridorwide connections to local parks and shared-use trails from SR 520’s new cross-lake bicycle and pedestrian path.
Natural areas enhancements
2011 – Grass Creek: Restored wetlands and shoreline habitat in the 68-acre Grass Creek site in Grays Harbor County. Removed a portion of earthen dike and re-established tidal channels (SR 520 pontoons were constructed in Aberdeen, Grays Harbor County).
2013 – Evans Creek: Restored about 32 acres of wetlands on land previously farmed at the confluence of Bear Creek and Evans Creek, near Redmond.
2014 – Yarrow Creek: Restored wetlands and rehabilitated the Eastside stream to improve fish and wildlife habitat. Also added eight large, fish-friendly culverts within SR 520’s Eastside corridor to improve fish migration.
2015 – Bear Creek: Improved roughly 16 acres of important stream and river-bank habitat for salmon by stabilizing creek bank, adding stream gravel and wood, and planting native vegetation.
2015 – South Lake Washington: Improved about four acres of lakeshore salmon habitat by planting native vegetation, removing decades-old industrial structures and enhancing near-shore habitats.
2016 – Cedar River Elliott Bridge Reach: Restored about five acres of wetlands, side channels, floodplain and river habitat for migrating fish, including Chinook salmon.
2017 – SR 520 East Approach: Improved about one acre of Lake Washington sockeye-spawning habitat. This area is located beneath the east end of the new floating bridge. Done by adding lakebed gravel, removing bulkheads and rubble, and restoring and replanting the shoreline.
2018 – Union Bay Natural Area: Improved existing wetlands and buffers, and created new wetlands – about 22 acres combined – within this University of Washington natural area northeast of Husky Stadium.
Additional enhancements
WSDOT Peninsula: We will enhance wetlands and wetland buffers, control invasive plant species and add habitat features within this six-acre WSDOT-owned property next to the Washington Park Arboretum. This mitigation will follow SR 520 reconstruction.
Mitigation Reserves Program Wetland: The King County Mitigation Reserves Program allows participants to pool financial resources for larger restoration projects with greater environmental benefits. WSDOT is contributing to the county’s program to mitigate for a portion of the SR 520 program’s impacts to wetlands.
Enhancing historical and cultural resources
WSDOT has worked with the community to assess and protect historic and cultural resources along the SR 520 construction corridor. We’ve also done this at other locations where we built components for the new floating bridge.
Our efforts include:
- Ongoing consultation with Native American tribes, local governments, resource agencies and others to identify potential cultural resources, understand program activities and develop appropriate mitigation steps where needed.
- Use of temporary work bridges and barges to minimize our construction footprint in sensitive areas as we construct replacement bridges and other permanent highway structures.
- Consultation with stakeholders to ensure that the project’s structural and landscape designs are compatible with the historic character of neighborhoods in the corridor.
- Involvement of an outside expert in designing new bridges within historically sensitive areas.
- Surveys and inventories of historic homes, including floating homes on Portage Bay.
- Preparation of nominations for listing the Montlake Historic District and Olmsted-designed parks and boulevards in the National Register of Historic Places.
- Consultation with stakeholders to develop interpretive signage sharing local history.
- Development of a website that details local history and includes curriculum materials developed to share this history with school-age children
Environmental document library
February 2021 - NEPA/SEPA reevaluation for Portage Bay Bridge and Roanoke Lid Project (PDF 1.3MB)
February 2021 - Revised Section 4(f) evaluation for Portage Bay Bridge and Roanoke Lid Project (PDF 2.3MB)
May 2020 - SR 520 Floating Bridge and Landings Project AKART Stormwater Study Final Report (PDF 24MB)
October 2019 - NEPA/SEPA Environmental Reevaluation: I-5 Design Refinements, Attachment 1 (PDF 1.4MB)
October 2019 – SR 520: I-5/Mercer St to SR 520/Portage Bay I-5 Interchange Improvements (I-5 Express Lanes Connection Project) Noise Discipline Report (PDF 5.5MB)
September 2018 - NEPA/SEPA environmental reevaluation: Wireless Communications Facility Removal and Relocation (PDF 35MB)
July 2018 - NEPA/SEPA environmental reevaluation: Montlake Market Closure and Demolition (PDF 1.11MB)
October 2016 - NEPA/SEPA environmental reevaluation: West Approach Bridge South and Montlake lid design refinements (PDF 3MB)
March 2013 - SR 520, I-5 to Medina: Bridge Replacement and HOV Project Final Construction Noise and Vibration Report (PDF 6.9MB)
December 2011 - SR 520, I-5 to Medina: Bridge Replacement and HOV Project Final Aquatic Mitigation Report (PDF 42.4MB) (revised February 2012)
- Addenda to this report are on file with WSDOT.
December 2011 - SR 520, I-5 to Medina: Bridge Replacement and HOV Project Final Wetland Mitigation Report (PDF 19.4MB) (revised February 2012)
- Addenda to this report are on file with WSDOT.
August 2011 – Record of Decision
June 2011 – Section 106 Technical Report
June 2011 – Final Environmental Impact Statement (FEIS)