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South Fork Snoqualmie River

King County, Washington

Roadway Over River


USDA Mt. Baker - Snoqualmie National Forest ServiceMowat Construction Company


CES Consulting Engineers



September 25, 2005

A historic bridge built in 1914 needed to be replaced along Forest Service Road 58 in the mountainous region of Snoqualmie Pass. The United States Forest Service wanted a quick installation and a bridge system that could closely resemble the original structure, designated a registered historic bridge for its use on the Yellowstone Trail.

In the first phase of the project, consulting engineer CES completed replacement design type, size & location and a preliminary engineering report for the original 90- foot steel truss bridge. Section 106 historical evaluation, which included a preliminary design of existing truss strengthening, hydraulic analysis and approach roadway realignment design were also part of the scope.

After evaluation, the USFS signed a contract with Mowat Construction for a design-build project that utilized a Contech prefabricated truss system and an innovative retaining wall system with rock anchors for the bridge replacement. The custom bridge was designed as a replica down to every specific detail, including the wood deck. The project was successfully constructed in a two-month window in 2004.


Technical Description:

  • Width: 26 - ft.
  • Span: 126 - ft.
  • Style: Custom204
  • Finish: Painted Steel
  • Decking: Concrete

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