Why did the deer cross the road?

Well… to get to the other side.

A mule deer buck rocked back on its hind legs, beginning a jump over a guard rail onto a paved road.
Mule deer buck preparing to cross the road. WSDOT photo.

Anyone who’s traveled on Interstate 5 through Washington knows that it’s not exactly a remote travel way. In just a few minutes’ time you can pass through multiple cities or towns, each offering their own assortment of restaurants, retail, and services. If you happen to live in one of the increasing number of communities located near the interstate, you’re a quick drive away from access to a travel route that can connect you with the entirety of western Washington.

That’s great for Washington’s human residents, but wildlife has little use for such amenities. Animals need ways to access resources like food, water, and shelter, and they can’t just take the nearest off-ramp to stop for lunch. Human travel corridors sometimes impede the movement of wildlife across habitat — as is the case for much of I-5.

An aerial view of a six-lane highway with dense forest on either side.
An aerial photo of the area identified in the southern Interstate 5 corridor as having potential for improved habitat connectivity. WSDOT photo.

However, an unassuming piece of ground near Castle Rock stands in contrast to much of the developed lands to its north and south. Shaded by timber and carved with hiking trails, the forest flanks I-5 on either side. The interstate cuts through this forest for about six miles before the timbered landscape gives way again to buildings and development. Thousands of people drive right past this area every day without a second thought — but a group of wildlife scientists and transportation experts have come together over a shared understanding of this place.

This landscape has been identified as one of the most promising locations in the southern I-5 corridor for the installation of wildlife crossings to connect habitat from the Cascades to the Olympics and Willapa Hills. A wildlife crossing, often created as either an underpass or overpass across a travel way, is designed to allow wildlife a safe place to move from one side of the road to another without having to navigate the flow of traffic. These crossings can be essential links between otherwise isolated areas of wildlife habitat, allowing animals to access new resources and disperse across their landscape safely.

A sizable wildlife crossing overpass surfaced with grass and other foliage crosses a six-lane divided highway in the forest. Mountains and a lake can be seen in the distance. Less noticeable are two underpasses further along the highway.
Example of highway wildlife crossings on I-90 in Washington. The conspicuous overpass, as well as two underpasses seen further in the distance along the interstate, allow wildlife safe crossing over or under the roadway. WSDOT photo.

With state-managed public lands to the west and private timber land to the east, the property near Castle Rock is unique. Many areas along Washington’s southern I-5 corridor are becoming increasingly developed, made up of a combination of many landowners. At this property, however, a small group of landowners control a near contiguous stretch of undeveloped habitat.

Many species of wildlife, both big and small, have been seen using the habitat along this stretch of highway. Game cameras deployed along this portion of I-5 by the Washington State Department of Transportation (WSDOT) have recorded elk, deer, cougars, coyotes, and porcupine, along with a host of other smaller mammals in the forest just off I-5. Although these animals come right up to the interstate, few successfully cross this busy stretch of highway. In one example, scientists with the Olympic Cougar Project recorded a GPS-collared male cougar traveling over an eight-month span, starting in the Olympic Peninsula and moving down through southwest Washington. Although on many occasions it came close to the interstate - including encountering this important stretch of I-5 - it always retreated in the direction where it came.

A collage of four images of a cougar on a trail camera. Three of the photos are black-and-white taken at night; one image is in color, taken during the day.
Cougars are one of the wildlife species that have been seen utilizing habitat in the southern I-5 corridor. In the top right photo, vehicle headlights from I-5 can be seen in the background behind the cougar. WSDOT photo.

Individuals from state, tribal, and nonprofit groups have come together to see what can be done to secure this property for a wildlife crossing. Among those joining in on the conversation are representatives from the Washington Department of Fish and Wildlife, WSDOT, Conservation Northwest, the Olympic Cougar Project, and the Cascades to Coast Landscape Collaborative.

The first step to making this wildlife crossing a reality is to complete a Feasibility Study to determine the potential for such a structure to be successful. Previous habitat use modeling will be beneficial in this effort; such modeling has already shown that this location provides some of the greatest possibility for wildlife habitat connectivity in the southern I-5 corridor in Washington.

A trail camera image of a cow elk standing in the forest, spotted sunlight streaming down to the forest floor.
A cow elk caught on trail camera in the forest in the southern I-5 corridor. WSDOT photo.

Of course, no project can be made possible without funding. The findings of the upcoming Feasibility Study will help project partners support their applications for federal grants that award money to wildlife crossing projects, including a grant through the federal Bipartisan Infrastructure Law.

In the meantime, the project’s supporters will continue working together to discuss logistics, possibilities, and pitfalls that are inherent in the conceptualization of such a massive project idea. If you want to learn more about wildlife crossings over and under highways, contact WSDOT’s Habitat Connectivity Biologist Glen Kalisz. To learn more about wildlife habitat connectivity, contact a WDFW habitat biologist.



The Washington Department of Fish and Wildlife

The Washington Department of Fish and Wildlife is dedicated to preserving, protecting and perpetuating the state’s fish and wildlife resources.