Riley Slough Bridge 155

March 2019 Update

  • Construction is targeted to begin April 1, 2019
  • The bridge will be closed from April 1 through the end of the year
  • Additional construction and closure time may be needed in 2020
  • There will be no access across the bridge during construction
  • Traffic will be detoured 1.5 miles via Tualco Loop Rd


Riley Slough Bridge 155 is located on Tualco Road southwest of Monroe; it provides vehicular access to rural residences and agricultural areas in the lower Skykomish River valley. The current structure was built in 1930 and is 206-feet long and 18-feet wide. The bridge has had load limits posted on it since 2011 due to structural deficiencies, with a current sufficiency rating of 19.25 out of 100 due to deteriorating shallow timber piles and fragmentation of the concrete deck. The new replacement bridge will be 206-feet long and 32.5-feet wide to accommodate two 11-feet vehicle lanes and two 5-feet shoulders. The new structure will be a three-span concrete bridge positioned on driven piles.


Construction for this project is scheduled to take place in 2019.

Traffic Impacts

During construction there will be a 1.5 mile detour via Tualco Loop Rd.


Funding for the replacement bridge is 80% federal funding from the Bridge Replacement Program (BROS), and 20% from the Snohomish County Roads Fund. The total project cost $4.4 million.

Environmental Review