How Our Network of Roadways Has Altered the Natural World

Less than one percent of the US is covered in pavement. Although it may feel like roadways, highways, back lanes and city streets are omnipresent—inevitable, in some ways—they actually cover a shockingly small portion of the country. 

But the impacts of roads? Those go on for miles. As Ben Goldfarb writes in his new book, Crossings, the “road effect zone” covers about 20 percent of the country. “Park your car on the shoulder and bushwack half a mile into the woods, and you’ll still see fewer birds than you would in an unloaded wilderness. Hike two miles more, and you’ll still see fewer mammals. If you’re a Kerouac reader, you grew up steeped in the dogma that highways represent freedom. If you’re a grizzly bear, they might as well be prison walls.”

Goldfarb traveled across the country, and the globe, to learn more about how roads have shaped not just our communities but the natural world around us. Animals, both on land and in the waters, have a harder time migrating to food or to mate when surrounded by roads. Road salt is leaching into our water, contaminating the streams. The noise pollution from roads has changed the way birds and insects interact with neighboring forests. 

As Goldfarb discovered, roads may be nearly invisible to the modern human, just another necessary part of everyday infrastructure. But to the other species on this planet, roads have fundamentally changed their existence. 

Goldfarb spoke with Modern Farmer about his new book, how roads have impacted animals and agriculture and where we might go from here. This interview has been lightly edited for length and clarity. 

Modern Farmer: Let’s start with the basics. Your book talks a lot about “road ecology.” What is that?

Ben Goldfarb: Road ecology is the field of scientific study that looks at how roads and other transportation infrastructure affect nature and what we do about those impacts. The most obvious one is the dead animal lying by the side of the highway. A lot of road ecology is about why roadkill happens and what its effects on populations are and how to prevent it. But you know, it’s also a lot bigger than that. It’s about how roads disrupt animal population distributions and migration patterns and how road noise affects ecosystems and how all of the road salts that we apply changes waterways. So, it’s kind of a daunting vast field of study in some ways.

MF:  Why do roads have such an outsized effect on the world around them, considering that they actually take up such a small amount of physical space?

BG: It’s a good question. There are a couple of reasons that come to mind. First is that even though roads themselves don’t take up a huge amount of spatial area, they inflict habitat loss at a kind of gigantic scale. The example that always comes to mind for me are these migrating herds of mule, deer, elk and pronghorn antelope that we have in Colorado, where I live. For those herds, which have to migrate across the landscape to reach food and resources at different times of the year, roads can be a total impediment to their movement. There are some really heartbreaking cases of herds that starve because they can’t reach certain key valleys in the winter. So, for those animals, the road is 100 feet wide, and yet, it’s denying them access to millions, potentially millions of acres of good habitat. So, the road has this impact on the movement of animals that’s far vaster than its own physical form. 

The other thing I would say is road noise. Especially from big highways, noise is billowing away from the highway, and going half a mile or a mile into the surrounding ecosystem, and that noise has a huge impact. Animals have very sensitive hearing and tend to avoid noisy areas where the sounds of predator or prey might be obscured. 

MF: You do talk about wildlife crossings (built sections of highway that allow animals to safely pass over the top of or underneath the roadway) and the different ways they might look or feel and how they aim to facilitate animal movement. But there is also the notion of what makes a wildlife crossing successful. Just because the animal is moving doesn’t mean they’re going where they need to go, doing what they need to do. How do you actually track if a wildlife crossing is having the intended effect?

BG: You could say the wildlife crossing is working when an animal crosses the road using it. That does make intuitive sense. But, this has been documented in certain cases where the animals who are crossing are all young males, who are going back and forth looking for a female on either side of the highway and are unable to find one. So, maybe that crossing has been used dozens or even hundreds of times by young male bobcats or coyotes, but if they’re not mating, then they’re not contributing their genes to the population and the population might not be growing. 

There really haven’t been many or maybe even any studies that have rigorously shown a wildlife population increasing because of the presence of wildlife crossings. There’s still one more kind of level of research to be done, and that’s the level that would show real population responses to these structures.

Author Ben Goldfarb. Photography by Terray Sylvester.

MF: I want to talk a little bit about the intersection of roads and agriculture and ranching. In the book, you mentioned the anecdote of wildlife crossings in Wyoming and how they were actually really supported by ranchers, and I wanted to find out why ranchers were so supportive of the idea in that area.

BG: [In that instance], there was this campaign for a special license plate in the state, and the sales of the license plate would go towards wildlife crossings. That campaign to create the license plate was not really going anywhere until the big ranching association got on board and supported it. 

Of course, there are many ranchers who love wildlife, that’s a big part of the appeal. Many ranchers care about being good stewards of nature and ranch in harmony with the elk, deer and other critters who use those ranch lands.

But there’s also the linear infrastructure of ranching that’s all over the landscape. 

MF: You mean fencing? 

BG: Fencing, yes. And those fences have a real impact on wildlife mobility, they can prevent animals from moving successfully and equally across the landscape. Imagine a scenario in which the cattlemen association is supporting these campaigns and pointing the finger at highways as being the problem to potentially distract from the impact of ranch operations in restricting wildlife mobility. 

I think that’s the thing about country roads. In some ways, they’re this safe neutral state that all industries can work on together, because they’re not exactly anybody’s fault. They’re just the structures that are out there. And they’re very harmful, but we can lay the blame on [the roads themselves]. Because it’s a non-regulatory space. 

MF: Another section of the book that stuck with me looked at groups of people planting milkweed and other pollinator-friendly crops along highways and rest stops and attempting to make the roads more friendly for butterflies and other pollinators. It feels like there are these smaller interventions that we may not even be aware of as we drive but that are helping to combat the negative impacts of roads. 

BG: It’s funny because what gets all the press are these fancy and expensive wildlife crossings like the Liberty Canyon crossing near Los Angeles for mountain lions. It’s a $90-million project and it’s been written about 10,000 times. But there’s also just so much opportunity in existing infrastructure. 

We have all these culverts out there, probably a couple million of them, that funnel runoff and seasonal water under roads, and each one of them is a potential wildlife crossing. They’re just waiting for a little tweak. Little retrofits [to the culverts] are incredibly inexpensive and can do a lot to use the existing landscape. 

We have all these culverts out there … and each one of them is a potential wildlife crossing. They’re just waiting for a little tweak.

MF: Are the most negative impacts of roads reversible? Or is there something that we might be able to do, especially as regular citizens? 

BG: Are they reversible? I don’t know. You could build a great wildlife crossing, but that doesn’t address noise pollution or storm water runoff or the debris filling the culverts. As the total impacts are so diverse and so nasty, there’s no single thing you can do to prevent them all. So, we may solve a few of the problems, like roadkill and animal mobility, but that’s only part of the problem. 

We can prevent new construction in bad places. There are good examples of fighting those roads in the US. There are also numerous examples of fantastic uses of existing infrastructure. In the book, I talk about how the forest service operates the largest road network in the world. I don’t know if most people realize that all of these old logging roads are out there on the landscape, hemorrhaging sediments into otherwise pristine streams. These old logging roads have been obliterated by the forest service and various conservation groups over the years, so that’s a good example. 

I also talk about the removal of urban freeways as well. These sections of interstate were plowed through communities of color in the 1950s and 60s very deliberately. Now, some of these really harmful road sections are starting to be rethought and torn down and replaced. It’s an example of roads being unbuilt. They might seem permanent and inevitable, but they aren’t necessarily so. We have four million miles of roads, and the vast majority of that is not going anywhere, but we are capable of removing harmful sections. 

MF: You write that our infrastructure “no longer has the luxury of invisibility” because of climate change. Can you expand on that? 

BG: In all things we’ve done to modify landscapes, nature always fights back.

One example is Vermont, which has [had] gigantic rainstorms this summer, leading to lots of flooding. And all of these dirt roads in Vermont were just turning to mud, bleeding sediments into the river, and all of these culverts were getting blown out as they got filled with debris. These intense rainstorms destabilized Vermont’s road network. 

In Alaska, you can see pavement that’s fractured and buckled, because of melting permafrost beneath roadways. As that permafrost melts, the overlying infrastructure, the roads, [are unstable]. There are just all of these ways in which our changing planet is impacting our transportation network and revealing how shoddily built a lot of it really is.

Crossings will be released September 19 from W.W. Norton press.