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I-90 Center Roadway Study

In July 2005, WSDOT started analyzing how traffic on I-90 would be affected if we change the way the I-90 center roadway is used. We looked at different scenarios, including using the center roadway only for high capacity transit. (High capacity transit is a public transit system, such as rail, that can accommodate large volumes of riders.) Engineers completed this study to inform key Department of Transportation decision makers and project stakeholders who are examining future I-90 transportation investments.

Below is a link to the study in Adobe Acrobat portable document format (.pdf). You can download a free copy of Adobe Reader at the Adobe Web site. 

I-90 Center Roadway Study - July 2006 (4.65 MB)

The study addresses the following questions:

  • How will improvements on other freeways affect traffic on I-90?
  • What are the changes in travel time if the center roadway is converted to exclusive high capacity transit use?
  • How many more or fewer vehicles and people can I-90 move if the center roadway is converted to exclusive high capacity transit use?
  • How will changes affect Mercer Island surface streets and access?
  • How will other I-90 corridor improvements affect traffic?