WSDOT is in the midst of a several-phase project to widen SR 18 to four lanes from Auburn to I-90. This effort includes many interchange projects and other details, with the aim of increasing capacity, reducing congestion and improving safety.
WSDOT first completed interim safety improvements and then set out to transform what had been a two-lane rural road into a four-lane divided freeway. The work has been done in segments starting at Auburn Black Diamond Road.
Why is WSDOT
widening SR 18 from Auburn to I-90?
SR 18 is a crucial freight and people mover in southeast King County. Transforming a two-lane rural road to a four-lane modern freeway keeps traffic moving and improves safety.
The End Result
Thanks to completed Highway 18 projects, drivers are already enjoying a wider and safer SR 18 from Auburn to Maple Valley. When all corridor widening projects are complete, a four-lane divided freeway will extend all the way to I-90.
Project Benefits
• Safety. Replaces intersections with freeway interchanges; reduces likelihood of head-on collisions by building 48-foot median to divide opposing directions of traffic; constructs truck climbing lanes. Our data show that these improvements are significantly improving safety (pdf 343 kb) on SR 18.
• Congestion relief. Increases capacity by two lanes, remove intersections and signals that slow down traffic.
• Environment. Highway 18 projects build detention ponds to capture and clean highway runoff; offset wetland impacts by creating new wetlands or enhancing existing ones; replace narrow culverts with bridges to help fish swim up and down streams.
What is the project timeline?
• 1991 to 1994 -- WSDOT completes interim safety improvements, including new signals, median barrier and truck climbing lanes between Issaquah Hobart Road and I-90, updated lighting, signing and guardrail, and bridge widening.
• 1997 -- WSDOT completes widening from Auburn Black Diamond Road to Southeast 312th Street
• 1998 -- WSDOT completes the Issaquah Hobart Road Interchange and the bridge over the Raging River
• 1998 -- Crews complete Southeast 304th Street to Covington Way widening
• 1999 -- Southeast 312th Way to South 304th Street segment completed
• 1999 -- We complete Covington Way to 180th Avenue Southeast
• October 2002 -- Crews open the segment between 180th Avenue Southeast and Maple Valley. This project also extended Southeast 240th Street under SR 18 and removed the signalized intersection at 208th Avenue Southeast.
• September 2003 -- Construction starts on widening SR 18 between Maple Valley and Issaquah Hobart Road. This project will construct a new interchange at 244th Avenue Southeast and an overpass at Southeast 200th Street.
• 2004 -- WSDOT begins environmental review and preliminary design for SR 18 widening between Issaquah Hobart Road and I-90 and for I-90/SR 18 interchange improvements.
• November 2005 -- WSDOT presents its preferred alternative for SR 18 widening and I-90/SR 18 interchange improvements at public open houses in Maple Valley and Snoqualmie.
• Early 2006 -- Planting began to restore the SR 18 roadside between Covington Way and Maple Valley.
• Aug. 31, 2006 -- Crews open eastbound roadway between Maple Valley and Issaquah Hobart Road.
• October 2006 -- Opening of all four lanes on SR 18 between Maple Valley and Issaquah Hobart Road.
• April 2007 -- Planting to restore SR 18 roadside between Covington Way and Maple Valley completed.
• January 2008 -- Planting to restore the SR 18 roadside between Maple Valley and Issaquah Hobart Road completed.
Financial Information
This project is funded for construction of the widening up to the Issaquah-Hobart Road Interchange.
The project received $16 million in additional funds from the nickel funding package approved by the 2003 Legislature. This additional funding will provide for preparation of environmental documentation and other pre-design work for the segment from Issaquah Hobart Road to I-90 and fully funds the roadside restoration project from Covington Way to Maple Valley. The design, purchase of additional right of way, and construction between the Issaquah-Hobart Road Interchange and I-90 will need additional sources of revenue.
Corridor projects are funded through the following sources:
- 2003 Gas Tax (Nickel Funding) - $16 Million
- Existing Funds - $376.5 Million
- Total Funding Available From All Sources - $392.5 Million
How can I get more information?
Contact:
Gary L. McKee, Design Project Engineer
WSDOT Corson Project Office
6431 Corson Ave South
Seattle, WA 98108-1310
Phone: 206.768.5761
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