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I-90 - West Lake Sammamish Parkway - Intersection Modification

This project is complete
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Photo visualization of tear-drop shaped roundabout at westbound I-90 on- and off-ramps.

Click to see photo and graphic visualizations of what the roundabout will look like when it's complete.

I-90 roundabout
View photos of the roundabout under construction.


December 2014    

  • The roundabout was operationally complete on Nov. 14, 2013. Operationally complete means the roadway is open to traffic and the majority of work is complete.
  • This project was awarded to Graham-Marshbank, JV on March 20, 2013.
  • This project was built using the design-build method and in conjunction with a similar project on SR 92 in Snohomish County.
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We are building a roundabout at the intersection of the westbound I-90 on- and off-ramps and West Lake Sammamish Parkway S.E./180th Avenue S.E. and to reduce the risk of serious collisions.

As part of this contract, we will also install guardrails around bridge piers at nine Interstate 5 overpasses and one overpass on State Route 18 bridge piers.

Why is WSDOT improving the I-90 W. Lake Sammamish Parkway S.E. / 180th Avenue S.E. intersection?
The I-90 to West Lake Sammamish Parkway intersection was the site of 41 collisions from 2006-2010, including one fatal collision, 11 injury collisions, 14 rear-end incidents and 13  involving drivers turning from the off-ramp on to West Lake Sammamish Parkway (WLSP). The roundabout will help reduce the risk of serious collisions at the intersection by controlling the flow of traffic near the on- and off-ramps to WLSP.

The End Result
The new roundabout at West Lake Sammamish Parkway will help reduce the risk of serious collisions by controlling the flow of traffic near the ramps.

Project Benefits

Given the nature of the I-90 WLSP intersection, the number of collisions that occur within or near the intersection and increasing traffic volumes, a roundabout is an ideal solution for a few reasons:

  • Roundabouts reduce the number and severity of collisions because people drive more slowly through a roundabout.
  • With roundabouts, drivers can no longer run a red light or turn left in front of oncoming cars; two situations where severe or fatal injuries are common.
  • Roundabouts also help keep traffic moving because drivers only have to yield to others, not stop.

What is the project timeline?

  • Winter 2012: We began advertising the project for competitive bidding.
  • March 20, 2013: We awarded the project to Graham-Marshbank JV.
  • May 2013: We began construction.
  • November 2013: Project is operationally complete.
  • Spring 2014: Completion of final pavement markings and other work.

Financial Information

Financial Data for PIN 109052I
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $2,113
Total $2,113

Project signage will reflect the cost of construction engineering, project bid award and sales tax.

How can I get more information?
Mary Ann Reddell
WSDOT Project Engineer
Phone: 425-225-8725

Kris Olsen
WSDOT Communications
Phone: 206-440-4704

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