WASHINGTON, D.C. – A groundbreaking global study published today, July 31, 2025, provides the most comprehensive and definitive evidence to date that wildlife crossings are overwhelmingly successful at reducing deadly animal-vehicle collisions and restoring vital ecological connections severed by roadways. The decade-long research effort, coordinated by the Global Wildlife Corridor Initiative (GWCI), analyzed data from more than 120 dedicated crossing structures across 15 countries, confirming their critical role in modern conservation and transportation safety.
The report, published in the esteemed scientific journal Nature Sustainability, found that well-designed wildlife crossings—such as vegetated overpasses and spacious underpasses—can reduce collisions with large mammals by an average of 88%. For specific groups like deer, elk, and other ungulates, the reduction was a staggering 92%. The findings offer a powerful, data-driven argument for the widespread adoption of these structures as a standard component of infrastructure development in sensitive habitats.
“For years, conservationists and transportation planners have operated on strong local evidence and a great deal of ecological theory. Now, we have the global, longitudinal data to back it up,” said Dr. Alistair Finch, the study’s lead author and a senior research fellow at the University of Oxford’s Environmental Change Institute. “The results are clearer than we could have hoped for. These structures are not just a niche conservation tool; they are essential infrastructure for the 21st century, promoting safety for humans and survival for wildlife.”
A Decade of Data: An Unprecedented Global Scope
The ambitious study, titled “A Global Synthesis of Wildlife Crossing Efficacy,” represents a monumental undertaking in the field of road ecology. Researchers from the GWCI collaborated with national transportation agencies, universities, and conservation NGOs to synthesize data collected between 2015 and 2025. The project monitored a diverse array of wildlife crossings, from the iconic vegetated “green bridges” spanning multi-lane highways in the Netherlands and Canada’s Banff National Park, to large-span underpasses used by pumas in California and bears in Montana, and even canopy bridges designed for monkeys and possums in Costa Rica and Australia.
The sheer scale of the project allowed the team to control for variables like climate, traffic volume, surrounding landscape, and species type, leading to exceptionally robust conclusions. “We weren’t just looking at one bridge in one park,” Dr. Finch explained. “We aggregated data from high-traffic urban peripheries, remote mountain passes, and agricultural landscapes. The pattern was remarkably consistent: where you build a well-designed crossing, animal-vehicle collisions plummet and ecological connectivity is restored.”
The research team employed a multi-pronged approach to data collection. High-resolution camera traps documented usage patterns, while GPS collar data from hundreds of individual animals—including grizzly bears, wolves, moose, and jaguars—revealed how these structures were integrated into their long-term movement and territorial behavior. This was supplemented by collision data from transportation departments and insurance agencies, creating a complete picture of the crossings’ impact.
The Stunning Numbers: A Breakdown of the Findings
The data presented in the 300-page report is compelling. Beyond the headline figure of an 88% overall reduction in large-animal collisions, the study provides a detailed breakdown that underscores the effectiveness across different species and crossing types.
Key findings include:
- Large Ungulates: Collisions involving deer, elk, moose, and wild boar saw the most significant decrease, with an average reduction of 92% at sites with overpasses and associated funnel fencing.
- Large Carnivores: Elusive predators like bears, pumas, and wolves, which often require larger and more isolated territories, used the crossings consistently. Collision rates for these species dropped by an average of 85%.
- Economic Impact: The study calculated a significant economic benefit. Across the 120 sites analyzed, researchers estimated the crossings prevented more than 50,000 large-animal collisions over the decade. This translated into an estimated $235 million in avoided costs related to property damage, emergency response, and healthcare expenses for human injuries.
“The economic argument is now impossible to ignore,” Dr. Finch stated in a press briefing. “While the upfront cost of a wildlife overpass can be several million dollars, the data shows a clear return on investment over the lifespan of the structure. We are moving the conversation from ‘How can we afford to build this?’ to ‘How can we afford not to?’ It’s a matter of public safety, economic sense, and ecological responsibility.”
More Than Just a Bridge: Reconnecting Fragmented Ecosystems
While the reduction in roadkill is the most visible benefit, experts emphasize that the true ecological significance of wildlife crossings lies in their ability to combat habitat fragmentation. Roads, railways, and other linear infrastructure act as impenetrable barriers for many species, carving up landscapes into isolated islands.
“Think of a highway as a wide, fast-flowing river of concrete and steel. For many land animals, it’s just as impassable as a real river would be,” explained Dr. Lena Petrova, a conservation biologist with the World Wildlife Fund (WWF), who was not involved in the study but reviewed its findings. “This isolation leads to smaller, less resilient populations. It cuts animals off from food sources, potential mates, and the ability to migrate in response to seasonal changes or long-term pressures like climate change.”
This fragmentation can lead to a severe loss of genetic diversity. Isolated populations are forced to inbreed, making them more susceptible to disease and less able to adapt to environmental changes. “These wildlife crossings function as genetic lifelines,” Dr. Petrova continued. “They allow for the natural flow of genes between populations, which is absolutely essential for their long-term survival. The GWCI study provides the proof on a massive scale.”
A poignant example highlighted in the report came from a network of underpasses in Southern California. GPS tracking data showed a male puma successfully using a newly constructed underpass beneath Interstate 15 to move between the Santa Ana and Palomar mountain ranges—a journey that had been virtually impossible for decades. Genetic analysis later confirmed that he had successfully sired a litter of kittens in the new territory, injecting crucial new genes into a severely isolated population.
Design Matters: What Makes a Wildlife Crossing Successful?
The GWCI report also delves into the critical elements of design and placement, providing a blueprint for transportation agencies worldwide. The success of a wildlife crossing is not accidental; it is the result of careful, science-driven planning.
The study confirmed that the most effective crossings share several key characteristics:
- Strategic Location: Crossings must be situated along established animal migration routes or high-use corridors. The study found that structures placed based on extensive pre-construction wildlife monitoring were used up to 300% more frequently than those placed for engineering convenience alone.
- Appropriate Design for Target Species: There is no one-size-fits-all solution. Wide, open overpasses covered in native vegetation are ideal for herd animals like elk and deer, which are often wary of dark, enclosed spaces. Conversely, secretive predators like bears and cougars often prefer the cover of large, secluded underpasses.
- Essential Fencing: The report calls directional fencing—long stretches of high fence that guide animals towards the crossing structure—”non-negotiable for success.” Crossings without effective funnel fencing were found to be 60-70% less effective at reducing collisions, as animals would simply bypass the structure and attempt to cross the road elsewhere.
- Naturalization: The most heavily used structures incorporated natural elements like soil, logs, rocks, and native plants to mimic the surrounding environment, making animals feel safer and more comfortable using them.
“You can’t just drop a concrete bridge in the middle of a forest and expect it to work,” noted Dr. Petrova. “It requires a deep, interdisciplinary collaboration between engineers, ecologists, and landscape architects who understand the specific behaviors of the animals they are trying to help.”
The Path Forward: A New Standard for Infrastructure
The researchers behind the GWCI study hope their findings will serve as a catalyst for policy change around the globe. With governments increasingly investing in large-scale infrastructure projects, the report provides a powerful tool for advocates and planners to champion the integration of wildlife crossings from the very beginning of the design process.
In the United States, programs like the Federal Highway Administration’s Wildlife Crossings Pilot Program, funded by the Bipartisan Infrastructure Law, are already providing grants for such projects. The GWCI report is expected to bolster these efforts and encourage more states to develop their own comprehensive wildlife corridor action plans.
“Our goal is to see wildlife crossings become a standard, required component of all new major highway projects that intersect with sensitive habitats,” concluded Dr. Finch. “They should no longer be seen as an expensive add-on or a luxury. The evidence is now unequivocal: they are a critical investment in a future where both human communities and wildlife can thrive. They work, they save money, and they save lives—both human and animal.”
