Preserving Wildlife and Culture: The Ingenious Design of US Highway 93

Wildlife overpass spans US highway 93 in Montana

Revolutionizing Roadways: A Step Towards Human-Wildlife Coexistence

The Ingenious Design of US Highway 93

Driving north of Missoula through the Flathead Reservation on US Highway 93, one might notice a unique structure—a semi-circle arch overpass lush with vegetation. This isn’t just an ordinary overpass; it’s a wildlife crossing, designed to facilitate the safe movement of animals across the busy highway. However, what many motorists might not see are the numerous underpasses, wildlife exclusion fences, and jump-outs that form a comprehensive system to protect both wildlife and drivers.

This section of Highway 93 is a testament to innovative engineering and thoughtful design aimed at preserving local ecosystems. The overpass, along with 38 culverts, bridges, and underpasses, provide essential conduits for various species, including white-tail deer, mule deer, black bears, coyotes, raccoons, and bobcats, to cross the highway safely. These structures, complemented by exclusion fences, significantly reduce wildlife-vehicle collisions, which are a major cause of injury, death, and financial loss in the US.

The story behind these wildlife crossings is rooted in the early 2000s when plans to widen Highway 93 were proposed. The Confederated Salish and Kootenai Tribes (CSKT) advocated for a “context-sensitive design” that prioritized cultural, aesthetic, recreational, and natural resources. Their vision was to ensure that the road respected the land and the Spirit of Place, leading to one of the densest collections of wildlife crossing structures in the world.

The ecological, economic, and social benefits of these structures are significant. Wildlife-vehicle collisions cost Americans nearly $8 billion annually. Exclusion fences alone reduce these collisions, but when paired with crossing structures, they also ensure the long-term viability of local wildlife populations by maintaining habitat connectivity. This connectivity is crucial for genetic diversity, ecosystem dynamics, and the preservation of species that rely on long-distance migrations.

Research on the effectiveness of these structures has shown that they not only benefit large mammals but also smaller species and even invertebrates and amphibians. While crossing structures can’t fully restore pre-road construction habitat connectivity, they substantially increase road permeability, supporting the long-term survival of wildlife populations.

As more crossing structures are built worldwide, ongoing research is crucial to understanding their long-term impact. Initial studies indicate that wildlife use of these structures increases and stabilizes over time, but long-term monitoring is often lacking. Understanding how wildlife interact with these structures throughout their lifespan will inform future designs and improve their effectiveness.

Wildlife use of wildlife crossing structures on US93 North in Montana

Driving under the US Highway 93 wildlife overpass, one is reminded of the advancements in road ecology and the importance of these structures. The leadership of the CSKT has not only protected their land and culture but also set a precedent for future road projects. The field of road ecology has come a long way since the construction of the first wildlife overpasses in the 1980s, and the ongoing research will continue to enhance our understanding and improve the design of these critical structures.

This summer’s study on the culvert underpasses aims to contribute to the growing body of knowledge on wildlife crossing structures. These structures offer a promising solution for mitigating human impact on the environment, providing hope for a future where human-wildlife coexistence is not only possible but thriving.

Sources: