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a deer that appears young runs into a two-lane road within about 50 feet of a passenger truck towing a camper.
A deer runs across the road in New Hampshire.
Jim Cole/AP

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How cars ruin wild animals’ lives

If you love nature, consider not driving in it.

Marina Bolotnikova is a deputy editor for Vox’s Future Perfect section. Before joining Vox, she reported on factory farming for national outlets including the Guardian, the Intercept, and elsewhere.

At Future Perfect, we cover some of the greatest threats to life and well-being on Earth. For non-human animals, that usually means factory farming, which kills nearly 10 billion land vertebrates annually in the US alone.

But you might be surprised by another top human-caused killer of land animals, which may be second only to factory farming, although precise estimates are hard to come by: not hunting, or animal testing, or the fur industry. It’s cars.

When I first read about the horrifyingly high numbers of animals killed by cars, in a paper on roadkill by sociologist Dennis Soron, I couldn’t stop thinking about it. A commonly cited statistic says cars kill a million vertebrates in the US every day, and even this is likely to be a significant underestimate, according to environmental journalist Ben Goldfarb, author of the new book Crossings: How Road Ecology Is Shaping the Future of Our Planet. Yet cars and roads have become so naturalized that they hardly register on the list of priorities for animal welfare groups.

Crossings provides a badly needed corrective. Through the field of road ecology — the science of how roads and cars have reshaped nature — Goldfarb offers a lively account of the automobile’s transformative impacts on our life and culture, and on the non-human animals with whom we share the planet.

Book cover of Crossings: How Road Ecology Is Shaping the Future of Our Planet, shows aerial view of a curvy road running through a forest

“Roads are such a ubiquitous feature of our daily lives that we fail to recognize how catastrophic they are,” Goldfarb told me in a recent interview. “They’re kind of at the root of all environmental crises. Before you can poach an animal in a forest or clear-cut a forest, you need the roads to get the humans in and the product out.”

Crossings deserves to make the reading lists of policymakers around the world. It has profound lessons for the future of our transportation systems as we adapt to climate change: to protect the planet, switching to electric cars will not be enough. We also have to become much less car-dependent. “You can’t just electrify everything and expect to have suddenly created a benign transportation network,” Goldfarb told me.

The book could also have surprising implications for the hundreds of millions of Americans who travel to the country’s protected natural areas every year: if you value wildlife, you may want to rethink visiting them by car.

The following interview has been edited for length and clarity.

It may not be intuitive to people why roads matter so much for wild animals. Someone might think, why can’t animals just go to places where the roads aren’t, and stay there, to avoid getting killed? So how do you explain why roads are a conservation concern?

The lives of wild animals are defined by mobility. You have all of these different scales, both spatial and temporal, in which animals are moving. They’re moving daily, as they roam around their territories looking for food. They’re moving seasonally, as they migrate between different habitats as the year turns. They have to move, in some cases, once in a lifetime, to disperse through new territory, or in search of a mate.

All of those movements are absolutely imperative to the survival of both individual animals and wildlife populations. Roads terminate or truncate those movements, by killing animals directly, as roadkill, but also by creating a barrier of traffic, what some researchers call a “moving fence” — this kind of impenetrable obstacle that prevents animals from navigating their habitats. To take a really dramatic, stark example, there are herds of mule deer and pronghorn in Wyoming that starve en masse while trying to reach low-elevation valleys to find food in winter because highways have blocked their migrations.

Four mule deer face an underpass underneath an elevated highway
Mule deer approach a highway underpass in Wyoming, built to help them safely cross I-80.
Gregory Nickerson

Estimating the number of wild animals killed by cars is hard. But is there a best estimate that you’ve seen?

Not really. The number that you always hear cited is a million animals a day in the United States are killed by cars. I think that [estimate] is from the ’60s. I think it’s probably a vast underestimate. There have been more recent studies that have estimated the number of bird deaths [from cars] in the United States at up to 340 million birds a year. That’s birds alone — that’s not counting reptiles, amphibians, rodents. So we don’t really have a good estimate of daily roadkill, but certainly the number is enormous.

When I drive around in Wisconsin, the highway is often littered with the bodies of animals like raccoons, opossums, deer. I tend to see birds flying out of the way of cars just in time, so I had told myself that birds know how to avoid cars and are doing fine. But, as I learned from your book, that’s clearly not the case.

Yeah, no, not at all. That’s been one of the challenges of quantifying roadkill: It’s a largely invisible problem. Certainly, we see deer carcasses by the side of the highway and other large animals. But small animals are really hard to detect. And as a result, they’re somewhat invisible to us. I think that’s one of the tragic ironies of automobility, that speed is both the destroyer of wild animals and it also blinds us to that destruction. When you’re sitting in your little vehicular bubble cruising along at 70 miles an hour, you don’t notice all of those small, inconspicuous carcasses along the roadside.

Close-up of a dead barn owl in the middle of a road with a car with bright headlights approaching it.
A barn owl killed on the road in the UK.
Education Images/Universal Images Group via Getty Images

One of the really eye-opening experiences that I had working on this book was taking part in some bicycle surveys of roadkill in Montana. When you’re rolling along at 10 miles an hour and you’re much lower to the ground, rather than seated in the captain’s chair of an SUV, you see all of those small lives that you would never see at highway speeds in a car. I was struck by how many birds we saw: raptors, magpies, ravens, songbirds. The avian life along the side of the highway was really, really visible.

Apart from getting directly hit by cars, the noise of roads is also a huge problem for wild animals. Why is noise such an important factor?

Hearing is one of the most important senses that wild animals have. It’s absolutely imperative for both predators and prey. Many animals sleep with their eyes closed, but they all come awake when they hear the snap of a twig. If you’re an owl, you’re incredibly reliant on your hearing to detect the rustling of mice and voles in the grass. If you’re a mouse or a vole, you’re also listening constantly for the sound of a fox’s footsteps or an owl’s wings. Road noise masks those acoustic stimuli.

The classic study that showed this was the phantom road experiment. Researchers played the sound of traffic in a roadless wooded area in Idaho and found that many migrating birds avoided that area, and also that the birds who did use the area in the presence of road noise were in worse body condition than they would have been otherwise. The hypothesis there is that because they can’t hear predators because of the noise pollution from the traffic recordings, they have to spend so much time looking for predators, and as a result, they’re not foraging as much.

There are other issues. Noise pollution is stressful. It raises cortisol levels, just as it does for humans. It’s elevating our blood pressures and heart rates; it’s making us more susceptible to stroke and cardiac arrest and diabetes; it’s literally cutting years off of our lives. One of the powerful things about the science of road ecology is just how many parallels it has with human health.

One of the amazing inadvertent experiments was Covid, when all of this traffic and road noise was abruptly turned off. The rapidity of the animal response was incredible. The most powerful study was this study of white-crowned sparrows in the Bay Area, which basically found that, in the absence of low-frequency traffic noise, their songs became much more complex; they occupied different bandwidths. They immediately responded to the loss of traffic.

Cars are electrifying, and everyone likes to talk about how quiet electric cars are. Will electrification of the car fleet make much of a difference?

It depends on the speed. Beyond 35 miles an hour or so, most of the noise of traffic is actually tire noise. You’re hearing the grinding of the tire against the pavement, as well as the popping of little air pockets in the tread. So when you hear the hiss of the interstate highway a half-mile away, what you’re hearing is primarily tire noise. Tires have actually gotten a lot quieter over time and continue to do so, so that’s good, but it’s sort of impossible to eliminate all tire noise, which means that the electrification of the [car] fleet is not going to dramatically help at highway speeds.

Where it will help is in neighborhoods, below 35 miles an hour or so. But the silence of EVs is an issue in its own right. There are lots of pedestrian advocacy groups or groups that advocate for blind people who are concerned about the silence of electric vehicles. The federal government has requirements that EVs make artificial noise when they’re moving along at really low velocities.

The US car fleet, and cars around the world, are SUV-ifying: People are buying bigger, taller, heavier cars. We’ve written a lot about this at Vox as a safety concern for humans. How does that shift in car size affect wildlife?

It’s potentially a huge issue. The height of these giant SUVs and the massive hoods create this huge blind spot at the front of vehicles. You see all of these horrifying visuals where a toddler is standing in front of a Ford F-250 or something and is completely invisible to the driver. You could certainly imagine the same dynamic pertaining to coyotes and foxes and skunks and raccoons. If you can’t see a 5-year-old walking across the street, you’re certainly not going to detect a low-slung, small mammal or reptile crossing the street.

A lot of your book is about deliberately constructed wildlife crossings that go either over or under highways to allow animals to safely cross. What sorts of wildlife crossings exist, and what kinds of animals are cared about enough to create the political will to build crossings?

Wildlife crossings are incredibly effective, paired with roadside fencing that guides the animals to the crossings. Many different species use crossings very readily, and they’re really effective in reducing wildlife vehicle collisions and permitting animal migrations and movements to continue.

Aerial view over a bright green, grassy wildlife crossing that runs over a highway
Aerial view over a wildlife crossing in Germany.
Sven-Erik Arndt/Arterra/Universal Images Group via Getty Images

For the most part, the wildlife crossings that we’ve built are aimed at large, common animals that endanger driver safety, like deer and elk and moose: the animals that will wreck your car and maybe end your life if you hit them. We need more of those. But we also need more crossings that benefit the animals that don’t kill drivers on a regular basis, especially reptiles and amphibians, which are some of the most road- and car-endangered groups of animals in the world.

There are turtle culverts and toad tunnels out there, but they’re few and far between. There’s a lot of focus on wildlife crossings that pay for themselves, that prevent enough car crashes to recoup their own construction costs. But I think we’re also starting to see the rise of wildlife crossings that are aimed at conservation, rather than cost savings.

There’s a fascinating, evocative history portrayed in the book about the rise of automobility and how it came to be associated with going out into the wilderness and being in nature. Can you talk about how that history has shaped contemporary culture?

It really begins with this group of famous car campers: Thomas Edison, Henry Ford, Harvey Firestone, the tire magnate, and John Burroughs, the great nature writer and naturalist. In the early 20th century, they took their cars out into the wilds of Pennsylvania and other places, the Smoky Mountains, and all the newspapers rapturously reported on Edison and Ford’s adventures in nature. Those guys made car camping seem like this yeoman, manly pursuit and really excited the nation about car camping.

black-and-white photo of four men outdoors
Edison, Ford, Firestone, and Burroughs go camping.
Courtesy of The Henry Ford

And then it was those legions of car campers in the early 20th century who helped to create and expand the national parks network, and the creation of many, many campgrounds in national forests. Cars were the way that we got back into nature and connected with wildlife and saw America’s natural heritage. It’s kind of amazing to think about how much work the National Park Service did to court those automotive tourists, building giant new roads through the national parks and creating campgrounds and cozying up to the American Automobile Association.

The car has, ironically, contributed to the conservation of these places. I think there’s no question about that. National parks became America’s most loved landscapes because they were accessible to millions of people in their vehicles. But that’s the irony of roads and cars: The forces that have been tied to conservation for a century are the same things that are endangering those natural places. Roadkill is, unfortunately, rampant in national parks. Road noise remains a big issue in national parks, and the Park Service is very focused now on addressing those impacts. Parks are places where animals are safe from hunting and development and other forces, but they’re not safe from cars.

Humans venturing into nature via car isn’t necessarily good for the wild inhabitants who live there. How do you think about that practical ethics question for Americans who visit national parks? Is there an argument that we shouldn’t go into wild places [by car] at all?

It’s something I think about a lot and feel incredibly conflicted about. Last night, my wife and I were driving back from a beautiful hiking trail, and I hit what I think was an owl. I felt absolutely guilty and miserable about it.

[Humans] are inherently disruptive, and there is an ethical case for just staying the heck out of these places. Even though I certainly use roads to access nature, I also profoundly believe in the importance of roadless areas.

So I don’t really have a great ethical framework, besides to say that you’ve identified a hugely important issue, and one that in some ways I’m probably in denial about because I just love being in these outdoor spaces. But I also recognize that my wildlife tourism is a form of consumption. I’m very happy to see the wildlife, but the wildlife is not happy to see me, so it’s fundamentally selfish in some ways.

So far, my questions have been US-focused, but there’s obviously a global story here. Most road construction over the next century is not going to be in the US. Are other countries learning to not repeat our mistakes as they build out their road networks?

There are incredibly destructive highways planned in Southeast Asia and Africa and South America that are going to do a lot of damage to nature. On the other hand, there are some fantastic examples of innovation occurring in non-Western countries. Because they don’t have our calcified road network, they can be more creative than we are. One of my favorite examples is in India, where a new highway went through a tiger sanctuary. They elevated many miles of the highway on these giant concrete pillars, so instead of having the occasional wildlife underpass, the whole highway is above the sanctuary and animals have the run of the place. That road is more ecologically sensitive and radical than anything we’ve done in the United States.

One chapter of the book is set in Brazil, where I visited a park where the road had actually been engineered to be really sinuous and curvy, both on the X and Y axes, to make people drive slower for the sake of animals. It’s this ecological sensibility that’s baked into the design of the road.

So there are absolutely things happening in places like Brazil and India and Costa Rica that American engineers should be paying attention to and learning from. In Brazil, everywhere you go, you see these rope bridges across highways for monkeys. We don’t have monkeys in the United States, but we have squirrels and pine martens and porcupines and lots of tree-dwelling animals that would also benefit from those kinds of canopy crossings.

Anything else you want to add?

We haven’t really talked about what a cause of suffering roads are. The large animals that people hit — the deer, the elk, the black bears — those animals don’t die instantly. They experience tremendous misery and suffering. There’s probably nothing that we do that causes more suffering to wild animals than driving. That’s something that the professional ecologist and biologist class doesn’t always talk about; they’re understandably very focused on animal populations. But the impact of roads on the lives of individual animals is profound.

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