Urbanization has affected nature in many ways — mostly negative. Natural spaces are becoming smaller with limited food sources. However, modern areas block migration and grazing routes. Because of this, creatures are forced to interact with the modern world. At best, they slow traffic and cause jams. At worst, they become roadkill. To prevent this, Sweden has joined the places building safe wildlife crossings.
Sweden’s Wildlife Crossings
Every April, Sweden’s main highway has to close. This is when hundreds of reindeer, watched by Sami herders, journey into the western mountains. The road has become busier, and if authorities don’t close it in time, the drivers spook the reindeers and cause traffic jams until the herders calm down the creatures.
“During difficult climate conditions, these lichen lands can be extra important for the reindeer,” says Per Sandström, a landscape ecologist at the Swedish University of Agricultural Sciences.
To solve this, Sweden decided to build multiple reindeer viaducts, also dubbed “renoducts,” to allow the creatures to cross with ease. These wildlife crossings can also benefit local lynx and moose. It opens a space that their ancestors were once accustomed to.
“The animals that will really benefit from this system are long-ranging mammals that are really not meant to survive in these small, isolated pockets,” says Sandström.
These renoducts aren’t a new concept. In Mexico, by the Yucatán peninsula, jaguars use custom-made underpasses to avoid hazardous roads. Millions of red crabs use specially-designed bridges to migrate from the forest to the beach every year on Christmas Island. Even in nature, canopy beds in the Amazon help porcupines, monkeys, and kinkajous steer clear of gas pipelines.
“When habitat is isolated, we can have an impact on individual animals where they might not be able to find water or food. We can also have an impact on the genetic diversity of populations,” says Mark Benson, a member of the human-wildlife coexistence team for Lake Louise, Yoho, and Kootenay at Parks Canada. 
Preventing Wildlife-Car Collisions
For context, 98 deer, multiple raccoons, three moose, two elk, and a cougar died on one highway in Utah over two years. That’s 106 animals killed in car accidents. There are 21 species in the U.S. — including Key deer and red-bellied turtles — that are endangered because of the frequent killings on the road.
And it’s not just the animals who suffer. According to the National Highway Traffic Safety Administration, about 200 people die every year in over a million car accidents in the United States. The risk of fatality and expenses depend on the animal being collided into. But these collisions are becoming more frequent.
“Over the most recently reported 15-year period, wildlife-vehicle collisions have increased by 50 percent, with an estimated one to two million large animals killed by motorists every year,” says Rob Ament, the road ecology program manager at the Western Transportation Institute (WTI) at Montana State University.
Building wildlife crossings can save money and the lives of animals and people. “You can get reductions of 85 to 95 percent with crossings and fencing that guide animals under or over highways,” Ament says.
These crossings are expensive to build, ranging from $300,00 to over a million. But not having them could be even more expensive. Wildlife collisions often cost about $4,000 per case. Then there’s the priceless factor of saving human lives and endangered species. 
These overpasses look like regular bridges from afar, but they are covered in natural plants to blend into the surrounding environment as much as possible. Underpasses often go unseen by passing drivers, but they are aiding smaller and more vulnerable creatures.
Designing the Wildlife Crossings
The Trans-Canada Highway in Banff is one of the most successful wildlife crossings.  Car collisions have decreased from about 12 per year to just 2.5, saving over $100,000. Banff now hosts six overpasses and 38 underpasses. Tony Clevenger, a senior research wildlife biologist at WTI, notices how different species interact with the crossings.
“Grizzly bears, elk, deer, and moose prefer big structures that are open,” he says. “Cougars and black bears prefer smaller, more constricted crossings, with less light and more cover.” This makes sense considering the animals’ natural habitats. For instance, black bears reside in forests, so they prefer a closed space to an open structure.
Knowing this helped design the crossings. “On one side we would plant trees and shrubs, and on the other side have areas that are open, planted with grass,” Clevenger says.
There is a learning curve to using the crossing, and it takes time for different animals to feel comfortable on it. After that, however, the crossing becomes part of the routine. Therefore, the offspring grow up accustomed to it, keeping the future generation of animals safe from the highway.
“We don’t want to just connect animals — we want to create ecosystems,” says Patty Garvey-Darda, a wildlife biologist with the U.S. Forest Service. This includes small species like mice and pika. “We are lucky. In Washington state, we still have all of our native wildlife species—even grizzlies and lynx. That’s not true of a lot of states. Wildlife crossings will help make sure that’s true into the future.” 
- “How creating wildlife crossings can help reindeer, bears – and even crabs.” The Guardian. Patrick Greenfield.January 23, 2021.
- “Genetic connectivity for two bear species at wildlife crossing structures in Banff National Park.” The Royal Society Publishing. Michael A. Sawaya, Steven T. Kalinowski, and Anthony P. Clevenger. April 7, 2014
- “How wildlife bridges over highways make animals—and people—safer.” National Geographic. Starre Vartan. April 16, 2019
- “This Is Why We Need Wildlife Crossings.” Tree Hugger. Noel Kirkpatrick. March 3, 2020