You’ve probably slammed on your brakes after a squirrel darted in front of your car. (Maybe, one time, you didn’t slam your brakes fast enough.) Imagine a road through a rainforest or a tropical savanna, a road teeming with not just passenger cars but logging trucks and mining equipment and heavy machinery, the carriers of industry. That is Brazil’s BR-262. Measured by roadkill, it is one of the earth’s deadliest roads for wildlife. BR-262 cuts across Brazil from the Atlantic coast to the Bolivian border and is causing the rapid decline of Brazil’s iconic giant anteaters through direct collisions and habitat fragmentation. And it’s one of many similar roads in Brazil, which has the fourth largest road network on earth.

For The Atlantic, Ben Goldfarb travels 112 miles of BR-262 to assess the disturbing impact roads have on wildlife, and how scientists and the burgeoning field of road ecology work to understand and moderate that impact. Roads do improve peoples’ quality of life, but there also are what he calls “the brutal costs of infrastructure.”

Often, practicing road ecology means knowing when a road shouldn’t be carved at all. Fernanda Zimmermann Teixeira, an ecologist at Brazil’s Federal University of Rio Grande do Sul, pointed out to me that no amount of eco-friendly engineering can blunt the habitat destruction that will follow the paving of certain Amazonian tracks. It occurred to me that, in a tragic twist, wildlife crossings and fences could even become a form of green-washing, a cynical tactic for laundering a harmful road’s environmental reputation. “We cannot talk only about mitigation—you have to talk about avoiding roads,” Teixeira said. “Passages won’t make any difference if we change the whole land use and burn everything.”

Yet new routes are coming, whether we’re prepared or not. The International Energy Agency has estimated that more than 15 million miles of new road lanes will be built by 2050, nearly 90 percent of them in the developing world—a trend the ecologist William Laurance calls an “infrastructure tsunami.” Many of the regions slated for massive road networks—Sumatra, Central Asia’s steppe, the Peruvian Amazon—harbor our planet’s most intact habitat.

Conservationists have staved off some especially frightening projects: A highway that would sunder the Serengeti’s wildebeest migration lies dormant, fought to a standstill by local activists. But the Hydra only sprouts new heads, forcing scientists into hard decisions. “The way I see it, many of these roads are going to be built whether we like it or not,” Rodney van der Ree, an Australian road ecologist who often consults with foreign governments, told me. He recently helped persuade officials in Myanmar (also known as Burma) to add underpasses to a highway that could disrupt the movements of leopards, tigers, and elephants. “From a biodiversity standpoint, they shouldn’t build the road at all,” van der Ree said, “but at least it’s a better outcome than it was.”

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