A mountain lion passes beneath the Hollywood sign at night

America’s ambitious bet on wildlife crossings

Written by:
May 31, 2022
Steve Winter/ National Geographic via Caltrans

America’s ambitious bet on wildlife crossings

On March 23, 2022, a young male mountain lion bearing a thick black tracking collar was struck and killed on California’s Pacific Coast Highway.

This animal was part of a 20-year study of the indigenous mountain lion population in the Santa Monica Mountains. The Santa Monica Mountains Recreation Area service, which operates within the National Park Service, posted an announcement of the unfortunate event on social media, stating that this was the 25th large cat and eighth within the study group to be killed by an auto collision since the study began in 2002. The young lion had been tagged for tracking only two weeks before its death.

Collisions between vehicles and wildlife attempting to cross major thruways have been ongoing problems in the state of California since the construction of the PCH and U.S. Highway 101—both of which skirt the Golden State’s coastline—during the postwar boom of the 1940s and 1950s. The California Highway Patrol logged more than 44,000 traffic incidents involving wildlife statewide between 2016 and 2020 alone. Large byways such as U.S. 101 have effectively bifurcated native wildlife habitats, stunting animals’ ability to seek food and grow their territory. Mountain lions, a protected species in California, are also wandering animals that constantly seek new territory and shelter away from man's encroachment.

Mountain lions are but one species expected to benefit from the construction of the Wallis Annenberg Wildlife Crossing near the city of Agoura Hills in Los Angeles County, the ground for which was broken on April 22 of this year (Earth Day).

When completed in 2025, the crossing will be 210 feet long and nearly 175 feet across—wide enough for as many as 12 lanes of traffic, were it being constructed for vehicular travel—making it the largest wildlife crossing in the world. It will be a vegetated bridge, planted with the area’s native flora and designed to blend seamlessly into the surrounding area, standing 17 feet above the 10-lane bidirectional U.S. 101 below.

When asked about the structural and aesthetic benefits of choosing a vegetated bridge design, Michael Comeaux, public information officer for the California Department of Transportation (Caltrans - District 7), told Stacker, “Designing a vegetated bridge structure has a number of differences from vehicular and pedestrian structures… We are accommodating a different type of loading. This structure must play host to several feet of soil and drainage media, and, in doing so, the [weight of the permanent structure of the bridge] becomes a distinct design factor. In addition, we are introducing water atop the structure for irrigation. We designed a drainage system and waterproofing for the necessary protection of the new structure and the freeway below, as well as for capturing the water that passes through the soil and routing it into the adjacent habitat areas, thereby reducing the potential impact on the local stormwater drainage system and providing a beneficial function beyond the immediate irrigation application.”

More than 60% of the project’s $88 million budget is coming from private investors, with the rest being publicly funded. The project is also receiving unanimous public support, notably from local Indigenous communities who have a long history of harmonious cohabitation with local wildlife.

A great number of native species will benefit from the crossing. Caltrans is developing a monitoring and evaluation plan in advance of actual construction that, according to Comeaux, “includes more than 50 individual species ranging from the California mountain lion to harvester ants.” But while Caltrans will have a series of target species associated with its monitoring plan, the ultimate goal is “a comprehensive ecosystem reconnection over the freeway that is inclusive of wildlife and native plant communities. While the structure will indeed be a crossing, it is predicated on the overarching goal of connection, [and] connectivity is important not just for mountain lions.”

Comeaux pointed to the aforementioned National Park Service study as a useful source of data in this regard. “National Park Service data has shown that bobcats and coyotes are also exhibiting significant genetic effects since [U.S. 101] was built,” he said, “Research continues to show that smaller species including lizards and birds are affected by the habitat fragmentation caused by roads and urban development. Without a safe and sustainable wildlife crossing, movement between these remaining areas of natural habitat is severely restricted and wildlife within the Santa Monica Mountains is essentially trapped.”

In recent years, studies for the crossing identified eight target species: mountain lion (Puma concolor); bobcat (Lynx rufus); coyote (Canis latrans); dusky-footed woodrat (Neotoma fuscipes; Neotoma lepida); western fence lizard (Anaxyrus boreas); western toad (Anaxyrus boreas); mule deer (Odocoileus hemionus); and wrentit (Chamaea faciata). It is expected that further species will be identified via continual analysis throughout the construction phase of the crossing.

While this crossing is an important investment, it is limited to a single location. To ensure similar projects happen across the state, Gov. Gavin Newsom signed a budget in June of 2021 that earmarked $61 million toward highway wildlife crossing development (including nearly $7 million for the Wallis Annenberg). Wyoming, Texas, Virginia, Florida, Oregon, and Massachusetts are also funding wildlife-crossing research.

With the Biden administration’s infrastructure package devoting approximately $350 million toward animal-focused infrastructure development, the continued design and construction of crossings such as the Wallis Annenberg have a renewed chance of increasing safety for wildlife and highway travelers. Stacker used news and government reports to look at how other wildlife crossing efforts have affected human and wildlife communities.

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Wildlife passage bridge over highway
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Education Images/Universal Images Group via Getty Images

Wildlife crossings were developed to protect wildlife species and humans

Over- and undercrossings follow the traditional construction design of single- or double-span arch or beam bridges. Wildlife crossings do not need to withstand the weight of vehicular traffic, so bridge forms such as tied-arch, cable-stayed, or truss bridges are impractical. Tunnels, viaducts, and culverts are also commonly used, and they vary greatly in size, depending on the area they are installed in and the target species they are meant to serve. The Wallis Annenberg Crossing’s size, for example, was dictated by the large mammal species it is meant to serve. A crossing for marine or reptilian life would be a great deal smaller and would not likely be constructed as a bridge but as a culvert or causeway (a culvert within wetlands).

The concept of modern wildlife crossings was first developed in France in the 1950s as a means to aid hunters in flushing deer. The idea caught on and spread quickly throughout Europe. There is a particularly high concentration of crossings in the Netherlands: 30 crossings with 20 more in development for a country of just 17 million people and more than 16,000 square miles. , For context, the Netherlands is less than 7% of the size of Texas, a state with just 33 crossings across more than 268,000 square miles.

A study in the U.S. on the preponderance of wildlife-vehicle collisions has not been conducted nationally since 2008; however, some states are actively tracking the impacts of wildlife crossings on various wildlife species and on traffic safety, including Texas, Massachusetts, and Virginia. The Bureau of Labor Statistics’ National Transportation Library functions as a repository for those research studies.

A five-year study by the Colorado Department of Transportation employed motion-activated cameras at two wildlife overpasses, five underpasses, 13 wildlife guards, 14 escape ramps, and three pedestrian access points along State Highway 9. In the concluding mitigation report, published in May 2020, CDOT found that mule deer had a 96% success rate of safe passage while reports of wildlife-vehicle collisions plummeted by 92% and reports of animal carcasses from vehicle-involved incidents fell by 90%. And Texas, which has the largest wildlife crossing in the U.S., actively tracks animal foot traffic on many of its wildlife crossings. Multiple species have been observed using the crossings with success, from ocelots and coyotes to weasels and alligators.

Deer crossing busy road
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Jamie Hall // Shutterstock

Several states are actively investing in wildlife mitigation measures, including crossings

Qualifying the Federal Highway Administration’s 2008 report finding of 1,000 wildlife crossings existing in the U.S. is something of a challenge, as there has not been any subsequent study performed on a national level, nor is there a national database for these structures (as there is for vehicular bridges). However, states across the country have been actively investing in wildlife crossings and other mitigation measures in the intervening years.

In 2012, the Nevada Department of Transportation built nine crossings, including a 200-foot double-arch crossing, along I-80 and I-93 between the towns of Wendover and Wells, an area that sees thousands of mule deer cross each year. NDOT estimates that animal/vehicle collisions kill more than 5,000 animals and cost $19 million in accidents per year.

Panthers are of primary concern in Florida. A 2007 report from the Florida Fish and Wildlife Conservation Commission indicated that vehicle collisions were the main cause of the threatened status of native panther populations in the state, but that the installation of wildlife crossings was a primary factor in that population growing from an estimated 20-30 animals in the 1980s to an estimated 80-100 at the time of the report. Florida now has 60 crossings that have been specially modified for panthers. Many of these crossings are located in Collier County, a southern county skirting the Gulf of Mexico. Local news reports have offered anecdotal evidence of their success. The Florida Department of Transportation also released guidelines to aid localities in establishing wildlife crossings in their district.

Washington State’s I-90 Snoqualmie Pass project is one of the largest in the state’s history, reconstructing and expanding 15 miles of the interstate. Twenty-seven crossings have been planned along that stretch, of which two overcrossings and six wildlife underpasses were constructed during Phase 1 of the project, which completed seven miles of I-90. Remote-camera monitoring has shown the effectiveness of these passes; a 2018 construction update from the Washington State Department of Transportation calculated that more than 1,300 deer, 130 coyotes, and 95 elk had been photographed using just one crossing located at Gold Creek. Subsequent updates from Conservation Northwest, which administers the now-disbanded I-90 Wildlife Bridges Coalition’s mission through WSDOT, show that a variety of species have readily taken to the crossings. Bears, elk, bobcats, raccoons, and even weasels have all been spotted using them.

Man looking at remote camera images of wildlife using crossing
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Matthew Staver/For The Washington Post via Getty Images

The first wildlife crossing in the US was built near Beaver, Utah

While most of Utah’s approximately 60 crossings are small culverts designed for tortoises and other small aquatic life, the state built the very first wildlife crossing in the nation in 1975 over I-15 just outside the town of Beaver.

Utah's largest wildlife crossing rises over I-80 near Parley’s Canyon. The 50-foot-wide, 320-foot-long beam bridge was not expected to see much use from local fauna for at least a few years following completion in 2018, as it often takes animals a long time to recognize the bridge for what it is and to feel safe leaving their known territories. However, UDOT has seen an unanticipated rate of success: The bridge clocked 706 animal crossings in 2021.

The Utah Department of Transportation is partnering with the Utah Wildlife Mitigation Initiative to map the movement of wildlife throughout the state to understand more about how various species migrate or establish territories. UDOT tracks traffic statistics, which aids the Wildlife Mitigation Initiative in making recommendations for further mitigation efforts.

In 2020, UDOT and the Utah Division of Wildlife Resources installed six new mitigation points at various locations throughout the state, including a double culvert running underneath I-15 in Baker Canyon.

UDOT in 2022 earmarked $1 million of the federal infrastructure package for the installation of fences, underpasses, and other mitigation measures near I-80 and I-84, a notoriously treacherous area that sees frequent deer and elk traffic.

Caution wildlife crossing sign by highway
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Craig F. Walker/The Denver Post via Getty Images

Wildlife-vehicle collisions cost people in the US more than $8 billion annually

The FHWA’s 2008 report to Congress estimated that between 1 million and 2 million wildlife-vehicle collisions occur each year and cumulatively cost an estimated $8.39 billion. These costs include vehicle repairs, associated medical costs for drivers and passengers, towing fees, the time-dollar value of law enforcement services, carcass removal fees, and an estimated valuation placed on the animal that was struck and killed. As there has been no quantified data at the national level since this report, it may be likely that this overall cost estimate is much lower than what it actually is.

The FHWA report found that approximately 95% of wildlife-vehicle collisions result in property damage only, meaning aside from impact to the animal there are no human injuries or fatalities. As such, the cost associated with such a collision hovers around $2,600. The average cost of a wildlife-vehicle collision involving human injury or fatality balloons to more than $24,000, and a fatality upwards of $46,000. Collisions resulting in incapacitating or severe injury cost more than $230,000 on average, largely due to necessary extended care.

Approximately 200 people die and another 26,000 are injured annually from wildlife-vehicle collisions, according to a report from the Center for Large Landscape Conservation commissioned by the Pew Charitable Trusts.

A mountain lion passes beneath the Hollywood sign at night
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Miguel Ordenana via Caltrans

Building infrastructure that protects wildlife is supported at the state and national levels

Wildlife mitigation efforts have long been a bottom-up investment model, with individual states enacting projects and other safety measures with little mandate or incentive from the federal government. The Biden administration’s Infrastructure Investment and Jobs Act is, in essence, turning that funnel on its head by allocating approximately $350 million for a variety of wildlife safety and conservation projects.

In addition to $260 million in grant program funding recently doled out to states for general road safety programs, disbursements will be made over the next five years to states and municipalities in the form of competitive grants for designing and constructing wildlife-specific tunnels, bridges, culverts, causeways, fencing and walling, and other mitigation projects. The first $60 million will be distributed in 2022.

Conversely, the federal government’s previous multiyear plan, the Fixing America’s Surface Transportation Act, or FAST Act, did not stipulate that any of its $305 billion in overall funding be devoted to wildlife mitigation projects or research.

At the state level, numerous agencies are putting more skin in the wildlife mitigation game. Aside from the large-scale investment it is making in the Wallis Annenberg Wildlife Crossing, California has earmarked a further $54.5 million toward projects throughout the state. In March 2022, the Oregon state legislature passed a funding resolution devoting $7 million toward constructing wildlife crossings, the first time in state history funds have been so devoted. The state presently has just five crossings. Also this past March, a Colorado bill was introduced that would allocate $25 million to wildlife-crossing projects. The bill, if ratified, will advance many of the 25 wildlife infrastructure projects the Colorado DOT identified in its 10-year pipeline.

Further projects over the past decade, including those in Wyoming, Montana, and Nevada, have all demonstrated the effectiveness of wildlife crossings and other mitigation measures.

The Wyoming DOT in 2012 installed two wildlife overpasses, six underpasses, and 12 miles of fencing in the Trappers Point area that within three years of completion led to an 80% drop in wildlife-vehicle collisions, along with a 60% increase in territorial movement of mule deer and a remarkable 300% increase for pronghorn, according to a Pew report. There was also a 50% decrease in mule deer collisions along U.S. 93 and I-80 in Elko County, Nevada, resulting from the 2018 installation of bridge and tunnel crossings.

Montana has 122 wildlife crossings, 81 of which are located on U.S. 93, and while evaluative studies are ongoing as to their effectiveness, the state completed a study on 29 points of mitigation installed along U.S. 93 North. Findings, published in 2018, showed a 71% reduction in collisions with large wild mammals, a number that grew to 80% when data from the “control” portions (those without in-place mitigation) of the highway was included in the results.

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