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SR 520 - Environmental Stewardship

WSDOT is committed to building and maintaining a sustainable, integrated multimodal transportation system – one that supports healthy communities and economic vitality while protecting the environment. From the start, we plan and design transportation projects with the goal of minimizing their environmental effects or avoiding impacts altogether. During construction, we require best practices to preserve the region’s natural resources and promote public health and safety. When project impacts are unavoidable, we partner in initiatives to mitigate the impacts. 

The SR 520 construction program undertakes mitigation projects in a variety of locations to improve the region’s parks, natural areas, and historic and cultural resources.

Click to jump to a section below:
Building an environmentally smart highway
Promoting sustainability
Employing best management practices
Where to learn more

Related Pages:
Enhancing parks and natural areas
Union Bay Natural Area mitigation
Grass Creek mitigation
Evans Creek mitigation
Mitigation project map

Building an environmentally smart highway

Following years of community outreach and collaborative design refinements for the SR 520 corridor, WSDOT adopted construction plans that provide numerous environmental benefits for the region, including: 

Low-impact structural designs that minimize steel and concrete requirements, such as a West Approach Bridge North design that substantially reduced the number of in-water columns and the amount of concrete needed to build them.

new Eastside HOV lanes Dedicated transit/HOV lanes and median transit stops between I-5 and I-405, which our studies (pdf 12.5 mb) show will allow the highway to carry up to 17 percent more people during peak traffic, and 5 percent to 10 percent more vehicles.

A new cross-lake bicycle and pedestrian path (pdf 546 kb) that provides better connections to bus and light-rail stops, local bike paths, and a new Montlake Multimodal Center
A projected 10 percent reduction in greenhouse gas emissions (pdf 1.8 mb) within the corridor when compared to a no-build option due to improved traffic movement and increased transit ridership.
Eastside stormwater retension pond New stormwater management systems along the corridor, including on the new floating bridge, to capture highway runoff and improve water quality in local streams and Lake Washington.
A floating bridge design that allows retrofit for light rail should the region choose that option in the future.
Noise-reduction measures , including: quieter concrete pavement; noise-absorbing materials at lid portals; taller traffic barriers; quieter, encapsulated bridge joints to reduce highway noise for neighboring parks and communities; and noise walls on the Eastside.
Highway lids that reconnect neighborhoods, provide better transit connections, and increase community green space.

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Promoting sustainability

WSDOT strives to reflect sustainability as a core value. How? We’re designing and building an environmentally responsible, multimodal transportation system that can be operated and maintained effectively and efficiently for decades to come. What's more, our process for building that system demonstrates WSDOT’s commitment to sustainability. Examples include:

Contract requirements for WSDOT’s SR 520recycling dumpsters contractors to develop and implement ecologically sustainable practices, such as reducing, reusing and recycling construction materials, and managing their resources to reduce greenhouse gas emissions.
Reclaiming or using existing industrial/brownfield sites for construction of SR 520 bridge components or for needed corridor infrastructure, such as our new stormwater retention/treatment facilities. 

Read our 520 Sustainability Report in our Resource Library.  

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Employing best management practices

We’re following best practices during SR 520 construction to minimize the environmental effects of our work. A few examples include: 
Using specialized bubble curtains in Lake Washington to reduce underwater construction noise from pile driving, which can harm fish.
Employing truck-wash stations in construction areas to reduce dust and keep streets and highways cleaner as our construction vehicles come and go. 

Erecting 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.

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Where to learn more

Read more about how we’re enhancing parks, natural areas, and cultural and historical resources.
View an interactive map showing many of the SR 520 mitigation projects
Read a broad overview of our environmental initiatives. (pdf 3.25 mb)

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