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SR 520 Program - Environmental Process

WSDOT strives to deliver effective transportation solutions while minimizing effects on the community and natural surroundings. Our environmental analysis will ensure that environmental values are integrated along with other factors in planning, design and construction phases of the SR 520 Bridge Replacement and HOV Program.

Follow the below links for detailed information for each project of the SR 520 program:

  1. I-5 to Medina: Bridge Replacement and HOV Project
  2. Medina to SR 202: Eastside Transit and HOV Project
  3. Pontoon Construction Project

Will the SR 520 program improve the environment?

The SR 520 Bridge Replacement and HOV Program benefits the environment in four key areas: 

  1. Noise walls help to significantly reduce the effects of highway noise on neighborhoods and parks near the highway. 
  2. Stormwater treatment facilities will significantly improve water quality by treating stormwater that currently runs into Lake Washington untreated. 
  3. A bicycle/pedestrian path will provide a non-motorized option for cross-lake travel, helping to reduce emissions and congestion. 
  4. Completing the transit and carpool lanes from Seattle to Redmond will move more people in fewer vehicles.


Wood ducks
Wood ducks in the Washington Park Arboretum.

How will WSDOT restore, enhance or preserve the areas of the environment that are disrupted by the program?

The SR 520 program team is working with tribal nations and state and federal regulatory agencies to make sure the program obtains necessary permits and complies with national and state environmental requirements such as NEPA and SEPA.

In order to comply with these regulations, we will study a variety of environmental effects, including air quality, construction effects, noise, water resources, wetlands and wildlife. We publish our findings in environmental documents. 

A blue heron in the Lake Washington wetlands 
A blue heron in the Lake Washington wetlands.

What documentation has WSDOT already completed?

To date, we have the completed the following environmental documentation:

 Lake Washington wetlands
Lake Washington wetlands.

Which environmental topics does WSDOT evaluate?

• Air quality
• Community effects
• Construction effects
• Economics
• Energy
• Environmental justice
• Fisheries
• Geology and soils
• Hazardous materials
• Historical and archaeological resources
• Land use
• Mitigation
• Navigable waterways
• Noise
• Public services and utilities
• Recreation
• Transportation
• Tribal fisheries and cultural resources
• Visual quality
• Water resources
• Wetlands
• Wildlife

What are NEPA and SEPA?

NEPA is the National Environmental Policy Act, and it went into effect in 1970. It established a process to ensure that information on the environmental effects of a federally funded project is available to the public and decision-makers before a project is implemented. For large projects, NEPA requires the preparation of an environmental impact statement that evaluates environmental effects and identifies any reasonable alternatives that could eliminate or reduce these effects. Smaller projects, or those with fewer impacts, may be required to develop an Environmental Assesment, or qualify for a categorical exclusion.

Washington's State Environmental Policy Act legislation went into effect in 1971 and established an environmental review process consistent with NEPA for all state projects that are likely to have significant effects on the environment.