What exactly is ‘road ecology’? In his fascinating book, Crossings, the environmental journalist Ben Goldfarb sets out to explain how road ecologists study the impact of roads on flora, fauna and the environment in general.
He starts with a striking example: swallows with long wingspans died out over only a few decades because they weren’t agile enough to dodge traffic. Road-induced evolution!
Goldfarb then gives us a primer on North American ungulates, which include pronghorn, white-tailed deer and mule deer. Road safety had prevented many humans being killed on the roads, but not deer. As early as the 1960s, Wyoming built four tunnels under the Interstate 80 (I-80) (p50) to help protect local wildlife.
Traffic density, we learn, is critical. Too little and the deer can cross safely, too much and the deer refuse to cross at all. However, medium volumes make it a killing field. The deer think they can cross, but they perish in the process.
It’s not as simple as that though. Underpasses suit some deer, overpasses suit others. Road ecologists learned by trial and error but only after some failures had daunted, rather than enticed, the deer.
Meanwhile, the freeways around Los Angeles have created islands where cougars (mountain lions) are trapped. In their natural habitat they had evolved so that young males sought a territory well away from their fathers who otherwise kill them. In the Santa Monica Mountains, however, these killings are the norm because there is no escape from the “island” (p68).
The Banff Overpass
The gold standard for overpasses was over the four-lane Trans-Canada Highway in Banff – a simple pair of precast concrete arches that allowed grizzly bears to cross the highway (p76). An overpass spanning the ten-lane I-101 in Los Angeles was more of a challenge, costing some $87 million. That project was inspired by a solitary celebrity cougar, trapped by the LA freeways in a sort of “Hotel California”. Ironically, the overpass benefitted other cougars rather than the one who inspired the project (p88).
‘Herps’ (reptiles and amphibians to the layman) initially got less attention than deer or squirrels. It soon became obvious that salamanders and toads needed even more protection as local populations got wiped out. Projects like “Help a toad cross a road” in the UK and turtle rescues in Florida and Texas saved countless such creatures (p98).
Goldfarb goes on to highlight the massive road building undertaken by the US Forest Service, which carved 370,000 miles of roads mainly for logging industry access. This caused mass deforestation and habitat destruction (p115).
Habitat Loss
The USA, like much of Europe and the developed world, has become accustomed to traffic noise. For humans it may be an irritant, but it also means habitat loss for species who avoid noisy roads. Motor bikes are particularly powerful deterrents for wildlife. In Idaho, the Phantom Road project, which blasted a forest with traffic recordings, showed unequivocally that wildlife was deterred and even physically damaged by the noise (p143).
I’m sure everyone has noticed that bug-splattered windscreens are a thing of the past. It’s not that cars are now more streamlined, but rather that there are far fewer bugs today. It’s what entomologists call “insect apocalypse” (p155). The planting of the prairies and the practice of mowing US Interstate verges killed off the flowers (especially milkweed) needed by the bugs. The mowing was eventually abandoned.
One iconic example of the precariousness of roadside habitats is the monarch butterfly, which migrates from Mexico to New England or California. The irony here is that the now unmowed verges provide the main habitat to feed the monarchs, yet the traffic on the interstate highwys kills millions of the butterflies. On balance, however, the “Monarch Highway” along the interstates saved more butterflies than it killed (p168).
Goldfarb goes on to describe the morbid sounding “Necrobiome”, which is indeed morbid in encompassing the carcasses of roadkill. He quotes the poignant example of a launch director at the Kennedy Space Centre ordering all roadkill around the launch site to be cleared away. This was because he had seen turkey vultures circling the launch of Discovery after debris had caused Columbia to disintegrate on re-entry. It worked; the vultures disappeared (p180).
The clean-up on many highways isn’t always done by humans. Birds do a really efficient job, although they too sometimes become roadkill themselves. Some humans scavenge and eat the roadkill. In Alaska a charity distributes carcasses to needy families (p188).
Cleaning Up
What’s more, roads carry other pollutants like the toxic chemicals that tyre manufacturers add to their products – and, of course, salt. So, even living beside roads harms wildlife (p270).
Taking Action
The native Indians of northwest America have been particularly impacted by the advent of roads. Their culture and survival is based on fishing their streams. Even a small road can block the flow of a stream vital for salmon migration.
A road engineer may build a culvert to let a stream under their road. However, these are often too small and get blocked by debris. A group of Native American tribes brought an action to force Washington State to repair the worst offending culverts by 2030. And they won (p202).
Tasmania has been labelled “the roadkill capital of the world”. One consequence of roadkill peculiar to Australia’s marsupials is that a joey may survive a crash that has just killed its mother. As if in response, caring for orphaned joeys is widespread in Tasmania. Tasmanians maintain that there is an intrinsic value in caring for something (p222).
Monitoring projects like the UK’s “Project Splatter”, meanwhile, provide a wealth of data from participatory (aka citizen) science. For example, we now know that a quarter of British otters carry a parasite which makes them bolder and more likely to risk a road crossing (p241).
New Technological Pathways
The impact of Autonomous Vehicles (AVs) will be massive, but in what way is puzzling road ecologists. AVs will be better at detecting animals. For example, Volvo’s elk detection has been adapted for kangaroos. However, Goldfarb maintains that there will be many more AV journeys – transporting goods rather than people (p242).
The developed world is paying for its self-destructive road building. The developing world, on the other hand, appears to be more responsible, showing the developed world how we should have planned our road building. For example, an elevated highway over the Indian jungle allows tigers free access. Likewise, São Paulo’s privatised roads provide for wildlife crossings and clear up roadkill.
Yet the scale of road building in the developing world is nevertheless massive: a veritable tsunami. One key driver of this is China’s Belt and Road Initiative (BRI) which builds roads to connect producers to Chinese markets (p268).
Reparations and Recovery
The unconstrained road building of the last century has not only impacted wildlife, it has also made the lives of millions of humans miserable, unsafe or even deadly – usually the less advantaged. America had a history of carving highways through cities, obliterating some black communities and separating others from the rest of the city.
Back in 1989, a viaduct in Oakland destroyed by an earthquake was re-routed and replaced with a boulevard. Others followed – a sort of ‘reparation’ for past wrongs. Goldfarb also cites the example of Syracuse in New York State where a project has now been approved to replace the Interstate 81 viaduct with street level boulevards and local streets (p282).
Road ecologists have coined the word “anthropause” to describe the effects of the COVID-19 pandemic on wildlife. With human movement restricted, wildlife recovered old habitats. Unfortunately (for wildlife), this was short-lived and road use soon returned to pre-pandemic levels. Goldfarb acknowledges that we humans need the freedom of automobile travel, but argues that we need to “reconfigure our extant highways to manage its harms” (p296).
Conclusion
Crossings is a thoroughly entertaining and immensely informative account of a world to which many are oblivious.
This book will inform a new generation of environmentalists on how best to achieve the goal of minimising the impact of roads on wildlife, and humans. I’m sure that every road ecologist will refer to this work. It is essential reading for scientists, engineers, legislators and, above all, politicians. The benefits of managing road development in line with the environment are proven. There is of course now a distinct danger that the Trump administration will view road ecology as an unnecessary luxury and withdraw funding in the USA.
I hope that Goldfarb or others will give us an update for 2026 on how road ecology is evolving, especially in developing countries.
Personal Postscript
For me, as an Englishman, it was a joy to discover so many new words from the American outdoors. But one I did recognise was “draw” (for a shallow gully) which features in the folk song Old Paint about guarding a herd of cattle: “They feed in the coulees (ravines) / They water in the draw”.
Also, I’m intrigued as to whether the crossings on my local trunk road improvement, A417 “Missing Link”, will be as effective as some of Goldfarb’s examples.
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