As my wife and I drove the Trans-Canada Highway to our day-hike locations, we grew excited each time we approached a fenced-off highway overpass adorned with vegetation. These were wildlife crossings, which include overpasses and underpasses for large animals, and can also include culverts, tunnels, and other structures. Our initial fascination with the idea of a grizzly bear or moose roaming over the highway while traffic blurred below quickly grew into a curiosity about the history and effectiveness of the crossings.
Most wildlife travels over large geographical areas to feed, mate, and den. Movement allows for genetic diversity, a necessary component of species survival. Highways fragment wildlife habitats, and high-speed vehicles pose a danger to wildlife. Ecologists and conservationists have documented fragmentation and other impacts caused by roads in wildlife corridors, including increased mortality due to wildlife-vehicle collisions. See Jochen A. G. Jaegera et al., Predicting When Animal Populations Are At Risk from Roads: An Interactive Model of Road Avoidance Behavior, 185 Ecological Modeling 329–48 (July 2005). Habitat fragmentation decreases movement from one habitat area to another and increases isolation, inbreeding, and the likelihood of extinction due to resulting losses of genetic diversity.
Wildlife crossings are designed to keep wildlife from entering highways while providing a safe means for animals to migrate from one segmented plot to another within a larger habitat area. Keeping wildlife off highways reduces wildlife-vehicle collisions to the benefit of both animals and humans. The Federal Highway Administration estimates that these accidents result in millions of dollars in damages, tens of thousands of injuries, and 200 human deaths annually. Fed. Highway Admin., U.S. Dep’t of Transp., Wildlife-Vehicle Collision Study 7–9 (2008).
In the 1950s, European countries built the first wildlife crossing structures. Today, the Netherlands alone has more than 600 wildlife crossings. Species known to use these corridors include deer, wild boars, and the European badger.
The United States eventually followed Europe’s lead due, in part, to federal and state laws that required identification and mitigation of impacts to wildlife as part of the transportation planning process. The National Environmental Policy Act (NEPA) contains the broadest reach of any federal statute for the consideration of environmental impacts in transportation planning policy and typically requires an assessment of ecologically critical areas and mitigation efforts. See 42 U.S.C. § 4332. Executive Order 11990 relates to NEPA and requires, among other things, that federal agencies consider “maintenance of natural systems, including conservation and long term productivity of existing flora and fauna, species and habitat diversity and stability.” Exec. Order No. 11,990, 3 C.F.R. 121 (1977). While wildlife crossings have not been the centerpiece of much, if any, federal litigation, it is no surprise that they arise as an element of broader attacks on the mitigation techniques set out in Environmental Impact Statements in NEPA litigation. See Laguna Greenbelt v. U.S. Dep’t of Transp., 42 F.3d 517, 533 (9th Cir. 1994) (affirming district court’s grant of summary judgment and rejecting plaintiffs’ argument that the agency “did not consider a proposal to bridge every canyon along the route with elevated highway segments to permit wildlife corridors” because “additional wildlife crossings were incorporated into the final design”). The Endangered Species Act may require a lead agency to consult with the US Fish & Wildlife Service to consider impacts to a listed species and its critical habitat for a transportation project. See 16 U.S.C. § 1536(a) (2011). Other federal statutes may be implicated during the assessment of the need for wildlife crossings, including the recently enacted Moving Ahead for Progress in the 21st Century Act, which includes “[t]he addition or retrofitting of structures or other measures to eliminate or reduce crashes involving vehicles and wildlife” within the definition of a Highway Safety Improvement Project. 23 U.S.C. § 148(a)(4)(B)(xvii).
Various state departments of transportation now provide guidance on incorporating wildlife crossings of all sorts, from overpasses to culverts, into the planning process. In 2007, the California Department of Transportation published the first version of its comprehensive Wildlife Crossings Guidance Manual to assist biologists, planners, and engineers in researching and identifying best practices for assessing the need for wildlife crossings in transportation projects. See generally Cal. Dep’t of Transp., Wildlife Crossings Guidance Manual (2007). Some states provide more abbreviated but no less important guidance. See, e.g., Fla. Dep’t Of Transp., Wildlife Crossing Guidelines (2008).
As these laws and guidance have developed, the use of wildlife crossings in North America has grown exponentially. California installed three of the earliest wildlife undercrossings on U.S. 395 as a response to increased vehicle-deer collisions in the 1970s. In the 1980s, regulators proposed thirty-eight wildlife underpasses along Interstate 75 in Florida to avoid impacts to the endangered Florida panther, and these crossings now successfully accommodate not only panthers but also black bears, deer, bobcats, and raccoons. Randy S. Krautz, Stephen R. Bittner & Tom H. Logan, Wildlife Crossing Handbook 4–5 (2010). In 2006, the Montana Department of Transportation, in coordination with the Confederated Salish and Kootenai Tribes, built forty-one wildlife crossings and sixteen miles of wildlife fencing on US Highway 93 North. Other structures in the United States allow wildlife to cross over Arizona Highway 260 and under the sixteen-lane Santa Monica Freeway. By one 2008 count, there are 684 terrestrial wildlife crossings spread across 43 states and ten Canadian provinces and territories in North America. Nat’l Cooperative Highway Research Program, Transp. Research Board of the Nat’l Acad., Report 615: Evaluation of the Use and Effectiveness of Wildlife Crossings 3 (2008).
Wildlife overpasses and underpasses are “[t]ypically the highest cost option” for mitigation impacts to wildlife as compared to other options, such as culverts, median barriers, signs, detection systems, and escape ramps. Cal. Dept. of Transp., Wildlife Crossings Guidance Manual 55–62 (2007). Given the expense, scientific methodology and accuracy must underlie planning choices. The National Cooperative Highway Research Program (NCHRP) issued a comprehensive report in 2008 that provides invaluable guidelines for the selection, configuration, location, maintenance, and monitoring of crossings. See generally Nat’l Cooperative Highway Research Program, Transp. Research Board of the Nat’l Acad., Report 615: Evaluation of the Use and Effectiveness of Wildlife Crossings (2008). The goal of the report is to elevate piecemeal and haphazard approaches to crossings as a mitigation technique to a more data-driven, ecology-based strategy. Much of the report focuses on the concept of “permeability”—the ability of species to move freely across a landscape—as the most important consideration in evaluating the implementation of wildlife crossings. Rather than focusing solely on areas of frequent wildlife-vehicle collisions, the report suggests that planners consider species’ dispersal distances and home-range sizes to “help restore landscape permeability across fragmented habitat networks” and improve safety. Id. at 2.
I didn’t know any of this while driving on the Trans-Canada Highway. It cuts through the heart of Banff National Park and the Bow Valley with two lanes in each direction. Millions of tourists visit the park each year and contribute to the ever-increasing traffic rates. Fences line the shoulders of the Trans-Canada Highway to keep wildlife off the road. Since 1982, Parks Canada has constructed forty-four crossings over or under the Trans-Canada Highway. The crossings include six wide, vegetation-covered overpasses and thirty-eight underpasses. Initial studies relied on cameras to demonstrate wildlife use of the crossings, but specifics remained elusive. Scientists could not determine whether a single animal was crossing many times or if many of a species were crossing only a few times.
Tracking increased and improved enough to demonstrate that the longer the structures are in place near Banff, the more wild animals will use them. As use has increased, traffic-related mortality of large ungulates, such as deer and elk, has decreased. As of 2007, scientists had documented approximately 84,000 crossings by deer, elk, black bear, grizzly bear, mountain lion, wolves, moose, and coyote in Banff. Grizzly bears, in particular, have taken longer than other species to adapt to the crossings. Tony Clevenger, Highways Through Habitats: The Banff Wildlife Crossings Project, 249 Transp. Research News Mar.–Apr. 2007, at 14, 17.
Until recently, scientists did not know whether bears were traversing the crossings for mating purposes. Last year, researchers at Montana State University demonstrated that bears are crossing the Trans-Canada Highway to mate with bears on the other side. Michael A. Sawaya, Anthony P. Clevenger & Steven T. Kalinowski, Demographic Connectivity for Ursid Populations at Wildlife Crossing Structures in Banff National Park, 27 Conservation Biology 721–30 (2013). Researchers collected 10,000 strands of bear-hair samples from barbed wire on the crossings for DNA testing between 2006 and 2008 and discovered that almost half of the black bears using the crossings bred successfully. One male black bear in the study mated with five different females and fathered eleven cubs during the study period. The researchers also found that one-third of grizzly bears that used the crossings also bred successfully—promising news for a species widely known for its low reproductive rates.
Crossings are by no means a cure-all for the effects of habitat fragmentation in Banff. At a cost of two to four million dollars per crossing, not everyone favors the construction of more wildlife crossings on the Trans-Canada Highway. Uncertainties about the effectiveness of the crossings remain, providing fodder for opponents, whether they seek to better protect wildlife or to increase development. Questions also remain about whether the crossings have, in fact, reduced bear mortality. And the crossings do not address other impacts to wildlife. For example, grain spills from the Canadian Pacific Railway have proven to be so attractive to wildlife that researchers are now testing the placement of electrified mats on the rails to shock animals that tread the tracks in search of food. Ben Goldfarb, No Crossing Zones: New Technology Keeps Bears Out of Harm’s Way, Conservation Magazine, Spring 2014.
But the Trans-Canada Highway and other highways in wildlife habitats are here to stay, as are the accompanying impacts and habitat fragmentation. The new study on the role of wildlife crossings in bear mating demonstrates that crossings can improve the conditions of wildlife coexistence with humans by decreasing a known impact of habitat fragmentation. My curiosity about wildlife crossings has evolved into a deep appreciation.