Social, Economic and
Sustainable Design Considerations
Project: Monte Cristo Bridge
WHPacific designed a low-cost bridge structure and recommended the project sequencing that allowed Snohomish County to reestablish access across the south fork of the Stillaguamish River. Heavy flows there caused a large section of the riverbank supporting the Monte Cristo Grade Road to wash away in 2003.
The project site lies near the border of the Mount Baker-Snoqualmie National Forest, a delicate natural environment that required special attention to potential environmental impacts. Other challenges included budget limits, aesthetics, pedestrian safety, future maintenance needs and a schedule imposed by the Federal Emergency Management Agency.
Several techniques helped resolve the complex set of challenges:
• Constructing the bridge solely from one side of the river and using the existing south abutment was possible due to the use of lightweight trusses.
• Using timber planks for bridge decking to allow rain to fall through, eliminating the need to construct stormwater pipes and catch basins.
• Designing for future migration of the river channel, leading to the strategic placement and design of the center pier and north abutment.
• Selecting materials such as weathering steel trusses to complement the setting and keep future maintenance costs low.
• Integrating a pedestrian refuge into the design, allowing pedestrians and vehicles to use the single-lane crossing simultaneously.
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