Ecology and Transportation

Abstract

The Washington State Department of Transportation's (WSDOT) I-90 Snoqualmie Pass East Project has presented WSDOT engineers with many unique design challenges when integrating the ecological needs of the area with the transportation objectives of the project. The project faces issues of capacity, deteriorating concrete pavement, unstable rock slopes, and road closures associated with avalanches; there is also a real need to improve ecological connectivity of the area. I-90 is a physical barrier to the north–south movement of fish and wildlife. Wildlife attempting to cross the Interstate present a safety concern to motorists, and the barrier that I-90 forms between upstream and downstream aquatic habitats affects fish passage and hydrologic processes. To identify areas where investments in ecological connectivity should be made, WSDOT worked with dozens of agencies that manage land resources in the project area to design bridges and culverts that improve wildlife and aquatic connections. Integrating ecological objectives presented many design engineering challenges because of the project area's unfavorable construction conditions. Trade-offs and compromises between WSDOT and land resource managers were needed to find suitable solutions to problems. Issues that required compromises included eliminating scour issues while maximizing restoration areas; improving ground conditions for foundations without impacts to wetlands, endangered species, and footprint; creating habitat connections while treating stormwater; and designing bridges for clearance and connecting habitat.