On the final leg of our recent ten-day road trip, we were cruising westbound across the Cascade mountain range of Washington state on interstate 90 and came upon the structure you see above. It was unlike any other overpass we’d seen and I wondered at the time whether perhaps it was some marker of the crest at Snoqualmie Pass. Turns out it was far more interesting and valuable: the new wildlife crossing constructed by the state Department of Transportation under guidance of an array of agencies and NGOs with expertise in wildlife and the environment.
This is the Keechelus Lake Wildlife Overcrossing, 150 feet wide, planned since the early 1990s, constructed 2015-2019, and now used by thousands of animals who would otherwise be trapped on one side of the freeway, or killed by speeding vehicles when they try to cross. Vehicle collision accounts for a staggering number of wildlife deaths, more so every year as human population and development increases.
The crest of the Cascades, largely national forest and national parkland, is a refuge for wildlife, but the construction of I-90 effectively bisected the state, isolating populations. Animals need to wander for food, to find mates, for dispersal, to find seasonal habitat, to escape the effects of wildfire and other dangers. Isolated populations lose genetic diversity and resiliency, threatening their survival as a species.
Wildlife crossings have been built in Europe since the 1950s but were slow to catch on in the United States, primarily due to financial considerations. In the past few decades we have picked up the pace, even in anti-tax anti-animal-welfare states, as the economic value of crossings has emerged.
In Washington state, that’s why the Dept of Transportation has included many of these structures in their construction projects, both overcrossings like this one and many more undercrossings, which are cheaper to build. Undercrossings are essentially long bridges with habitat below, often in spots where creeks flow through. Salamanders, fish, otters and such are far more likely to use undercrossings than small culverts. While more expensive to build, overcrossings are more attractive to some animals, and the combination saves a wider variety of wildlife.
There is ongoing video monitoring of these projects; you can see some clips of animals crossing below. Keep in mind, these are the big critters, there are many many more small animals not visible here but no less important.
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WSDOT is about halfway through rebuilding fifteen miles of I-90, expanding it from four lanes to six, incorporating crossings as they go. The crossings and funneling exclusion fences have cut way down on vehicle collisions already, saving many human lives and millions of dollars. Additionally, the undercrossings make it much less likely for avalanches to dump snow on the highway, directing it below instead.
Altogether, wildlife crossings are win win win in every sense.
Of note, $350 million in the 2021 Biden Infrastructure legislation is dedicated to wildlife crossings. There are other proposed projects in Washington hoping to tap into those funds, like crossings across interstate 5 in southern Washington near the Toutle and Cowlitz rivers. I-5 blocks wildlife from moving between the Cascades and the Olympics. There’s a huge amount of planning and time required to push proposals through though, and the funding is limited.
Below is a video describing the I-90 wildlife crossings in more detail, and some links to information:
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Connecting wildlife habitat in the Cascades, I-90 Wildlife Corridor Campaign (Conservation Northwest)
Wildlife crossings potentially save millions in Washington state (Washington State University Insider)
Animals need infrastructure, too (Vox)
Roadkill: vehicle collisions may be threatening the survival of some mammal populations (The Conversation)
Wildlife crossing on I-5 near Castle Rock could be key to species’ survival, advocates say (The Colombian)
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More wildlife video, I-90 crossings:
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