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State Route 9 Corridor Program


  • Between 2000 and 2017, we expect to invest $300 million to improve SR 9 through Snohomish County.
  • For more information, take a look at the SR 9 corridor project folio (pdf 2.0 mb).
  • Sign up for weekly e-mail updates on our construction projects in Snohomish County.
                                                           SR 9 Map
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SR 9 Snohomish Corridor MapState Route 9 extends 98 miles, from SR 522 north of Bothell to the Canadian border. The highway parallels Interstate 5 to the east as it winds through Snohomish, Skagit, and Whatcom counties.

Growing population, increasing congestion
Due to regional economic development and the demand for affordable housing, the population of Snohomish County increased by nearly 80 percent between 1980 and 2000. 

This population growth has increased traffic on SR 9 throughout Snohomish County. The highway is now an important corridor for both commercial vehicles and commuters. Current traffic volumes have exceeded the capacity of the two-lane roadway leading to congestion and delay during peak travel times. 

Congestion-related collisions - like rear-end and sideswipe collisions - have also increased along SR 9. From 2000 to 2003, there were an average of 395 collisions per year on SR 9 in Snohomish County. Between 2004 and 2007, that average had increased to almost 480 collisions per year.

Since 2008, the annual number of collisions has dropped to 370 per year. In that timeframe, WSDOT completed several major projects along SR 9, including widening and intersection improvements between SR 522 and 212th Street SE, 176th Street SE to Marsh Road, and Schloman Road to 268th Street SE.

The end result: Improving safety and reducing congestion

Between 2000 and 2017, WSDOT will invest $300 million to transform SR 9 into a wider, safer highway. We will widen the highway to four lanes in some areas, add turn lanes at key intersections to reduce the risk of collisions, install divided medians at select locations to prevent crossover collisions, and upgrade pavement markings, guardrail, drainage, culverts and lighting where needed. 

When we wrap up work in 2017, these targeted improvements will help relieve congestion, improve traffic flow and enhance safety throughout the SR 9 corridor.

Current SR 9 improvement projects under way include:

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