One of the most immediate impacts of a world without surface roads would be a huge freeing up of space across the globe.
In rural areas this could mean more land for farming or for rewilding, to help boost wildlife and pull carbon from the air. It would also mitigate one of the huge problems with roads: they fragment landscapes.
For animals, roads can act as a barrier, separating species from each other or from their prey. The global expansion of road predator networks threatens all apex conservation efforts, according to one recent paper, including by reducing their genetic connectivity and increasing poaching, with sloth bears and tigers the most at risk. Increased fragmentation is also leading to more carbon emissions, as it increases the amount of forest edges, where there is higher tree mortality.
Roads can also interrupt the flow of water, says Alisa Coffin, a research ecologist at the US Department of Agriculture. She points to the Tamiami Trail, a road connecting Tampa and Miami which had disastrous effects for the Everglades by blocking water flow, leading to an increase in wildfires and impacting plants and animals. “It’s an example of how a road was built without really understanding what the impacts would be,” Coffin says.
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Collisions between animals and cars are another big problem. Sarah Perkins, a Cardiff University lecturer, coordinates Project Splatter, a decade-old citizen science research project which monitors wildlife killed on UK roads. It receives about 10,000 reports of dead animals every year she says, but Perkins talks that’s a fraction of the real total. Some studies have put roadkill numbers at hundreds of millions a year in Europe alone.
Putting roads underground “could lead to less wildlife-vehicle collisions”, Perkins says – provided the animals didn’t use the tunnels. It would also remove light and noise pollution, which can affect animal behavior around roads, she adds.
Despite these huge ecological impacts of getting rid of roads, however, it would be in cities, which are predicted to hold 70% of the global population by 2050, where the newly freed-up space would have the biggest impact on people.
“Can you imagine how the cities will be transformed?” asks Tom Ireland, projects director of tunnelling at engineering company Aurecon. “If you want to revive the city centre, you pedestrianise the roads.” It would open up room for trees, linear parks, landscaping, pavement cafes and scores of other public amenities.