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SR 520 - Enhancing Parks and Natural Areas

About > Environmental Stewardship > Enhancing Parks

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Parks enhancements
Habitat enhancements
Historical and cultural resource enhancements
Where to learn more

The SR 520 program includes a wide range of projects to protect and enhance parks, fish and wildlife habitat, and sensitive natural, cultural and historical areas across the region. Some of these projects are completed, while others are underway or in the planning stage as part of the program’s phased construction schedule.

Parks enhancements

Within the densely populated SR 520 corridor, we work with communities to mitigate the environmental effects of our construction program, in part by making significant improvements to local parks. Some of our parks enhancements include:

Washington Park AboretumImprovements to the Washington Park Arboretum, including a new multiuse trail; restoration work to Arboretum Creek and the Waterfront Trail; a new north entry into the Arboretum with various trail and park enhancements there; and an enhanced SR 520 pedestrian undercrossing on Foster Island.

Ramps to Nowhere near ArboretumRemoval of SR 520 on- and off-ramps in the Arboretum and the never-completed R.H. Thomson Expressway ”Ramps to Nowhere,” which will reduce traffic through the Arboretum and create a more open and natural park area.

Funding for traffic-calming measures in the Arboretum.

Development of a new, four-acre public park along Portage Bay near the University of Washington.

Trail improvements in the Portage Bay area.

A new Bagley Viewpoint on the planned 10th Avenue East/Delmar Drive East lid.

Corridor-wide connections to local parks and shared-use trails from SR 520’s new cross-lake bicycle and pedestrian path.

Habitat enhancements

The SR 520 corridor not only includes dense urban and suburban areas, but rich and diverse natural areas as well. We are making substantial enhancements in many of these natural locations to offset the environmental effects of our reconstruction effort, including:

Evan Creek restoration siteWetlands creation and enhancement across the Lake Washington basin, including sites adjacent to Yarrow Creek, Bear Creek, and
Evans Creek on the Eastside, and on the west side in the Union Bay Natural Area, Magnuson Park, and the WSDOT peninsula. 

Fish-habitat enhancements, including wetland and aquatic rehabilitation at the Cedar River Elliott Bridge Reach, aquatic mitigation along Bear Creek and Evans Creek, channel and riparian restoration on Taylor Creek in South Seattle, and Lake Washington shoreline restoration projects at the mouth of the Cedar River, at Seward Park, and along SR 520’s east approach, as well as in the Grass Creek intertidal area in Grays Harbor County.
new fish culvert under SR 520Replacement of narrow culverts beneath the highway’s Eastside corridor with large-diameter culverts  that unblock fish passage and aid fish migration in local streams.
Restoration and enhancement of SR 520 construction sites after work is completed, such as shoreline enhancements along the floating bridge’s east approach and on Foster Island.

Historical and cultural resource enhancements

WSDOT has worked with the community to carefully assess and protect historic and cultural resources both along the SR 520 construction corridor and at other locations where components for the new floating bridge are built. Our efforts include: 

Project designs that avoid or minimize effects on historical and cultural resources. 

Consultation with stakeholders to ensure that the project’s structural  and landscape designs are compatible with the historic character of neighborhoods in the corridor.
Involving an outside expert in designing new bridges within historically sensitive areas.

temporary work bridge across Union BayUse of temporary work bridges and barges to minimize our construction footprint in sensitive areas as we construct replacement bridges and other permanent highway structures.

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. 

Surveys and inventories of historic homes, and preparation of nominations for listing in the National Register of Historic Places for Olmsted-designed parks and boulevards and the Montlake Historic District.

Where to learn more

Read more about how we’re promoting environmental stewardship

View an interactive map showing many of the SR 520 mitigation projects.
Read our complete Arboretum Mitigation Plan (pdf 2 mb) online.

Go to to learn more about the early history of the communities along the SR 520 corridor and the later construction of the highway. 

View our SR 520 Environmental Documents library, where you’ll find environmental impact statements, mitigation reports, studies on water quality and fish, and more.