SINCE OUR NATION’S earliest days, America has been fixated on our roads, be they yellow brick, high or low, or the one less traveled. The United States has 4 million miles of roads, covering a surface area equivalent to that of South Carolina. They represent freedom, possibility, connection, and even escape. They are the circulation system of our culture and economy, shaping where we live and work, how we transfer goods, how we access services.
But roads have another side as well: a harmful one. Roads are the site of 30,000 deaths every year, but even beyond the obvious dangers, the network has its own, unintended effects on the country. Roads erode soils, trap heat, and disrupt wildlife habitat; they are expensive to create and even more so to maintain.
We’ve long fantasized that ultimately we’d see roads disappear completely, as Doc Brown suggests at the end of the classic 1985 movie “Back to the Future”: “Where we’re going, we don’t need roads.” He’s talking about 2015, a time when, as we see in the sequel, people are flying in hovercraft. But as 2015 approaches, we still rely on roads as the backbone of our transportation networks, towns, and cities. As engineers, city planners, and “road ecologists” are realizing, we do need roads. We just need better ones.
A road may seem so basic as to be unchangeable — a strip of asphalt or concrete laid across the ground. But in recent years, researchers have started to ask imaginative questions
about how roads work and don’t work — not just in their immediate impacts, but in the way they affect animals, water, energy use, and quality of life for people. They have begun to propose creative, even radical solutions to the problems that roads can cause, using everything from better highway design to smarter asphalt to reduce roads’ harmful effects. And though it’s still in early stages, some of this work goes even farther, plotting a future in which roads are not just a necessary evil, but can bring unexpected benefits to the land around them.
WHEN YOU’RE DRIVING on a highway through a vast desert or forest, it can seem as if the road is an insignificant part of the landscape. But that’s an illusion. Though roads are conduits for one kind of movement, they’re barriers as well: they block ancient patterns of animal migration and cause countless wildlife deaths every year. They help spread invasive plant species by dispersing seeds and allowing them to gain a foothold along the roadside corridor, while fragmenting and isolating native populations. That isolation can disrupt usual breeding patterns, making populations less genetically diverse and more vulnerable to being wiped out by catastrophic events.
The ecological effects of roads extend beyond the road surface; Richard Forman, an ecologist at Harvard, estimates that one-fifth of the nation’s land is directly affected by roads. Noise from heavily trafficked roads can inhibit bird densities and breeding for several hundred yards on either side. The construction, use, and maintenance of roads causes erosion and spreads pollutants into surrounding air, soil, and water. Roads and related structures like culverts also disrupt water flows and wetlands, which can have far-reaching impacts on humans and other species. In fact, while roads may seem like an innocuous and narrow disruption, they actually amount to a re-engineering of habitat on a vast scale.
Forman is one of the founders of road ecology, the study of roads’ effects on ecosystems. The discipline was founded in the 1990s, and research from the field is finally beginning to yield practical innovations in road design. Joseph Burns, who works in transportation ecology and species protection for the National Forest Service, says that a paradigm shift is taking place in the way highways are constructed. “Instead of breaking up systems — whether human communities or natural processes — now they’re more permeable.” To take one example, traffic collisions had been one of the top killers of Florida’s panthers, one of the most endangered animals in the country. When a series of highway underpasses was built along I-75 in the 1990s, the panthers began using them for safe passage across, lowering collisions on the highway.
Wildlife overpasses and underpasses now straddle highways and roads throughout the country, particularly in the Rockies and in Florida, where large animals are frequently hit by cars. Bill Ruediger, a wildlife consultant in Montana who has been involved in over 100 wildlife crossing projects over the past decade or so, says that animals readily learn to use these structures. Although the will to build crossings is highest where collisions with large animals cause injuries and cost money for travelers, conservation activists and biologists are also looking for solutions for small animals like salamanders and frogs, whose survival depends on the connection of far-flung populations.
The flow of wildlife is not the only thing historically disrupted by roads: there’s also the flow of water. Burns says that engineers are now taking waterways into account in considering how to plan and rebuild roads. Where highways once barreled through floodplains, they are now built to bridge them, which preserves water stores and habitat while also protecting roads from costly washouts. Roads that work with water systems, he says, “are adaptable and more cost effective.” He adds that if designed correctly, such roads can even provide a service, withstanding the peak flows while helping to hold water in dry times.
THE STUFF OF ROADS — concrete and asphalt — has been used for centuries, and these simple materials have facilitated an astonishing degree of mobility for people and goods. But traditionally paved surfaces create a number of problems. They prevent rainwater from reaching soils, instead sending polluted runoff into nearby waterways. The high temperatures of pavement in summer make cities hotter, and the warm runoff from highways heats up nearby pools and streams, changing the species that can survive there. And producing them is problematic too: Concrete production is a major contributor of greenhouse gases, and asphalt is made with petroleum products. Both materials are becoming dramatically more expensive as demand for construction materials rises worldwide.
To mitigate these problems, road construction is already changing. For one thing, a growing percentage of asphalt is reclaimed. In some cases, recycling can be done on the spot, with pavement torn up, either milled and compacted or heated and remixed, and then relaid. In the past few years, states including Massachusetts have begun to use a technology called “warm-mix asphalt,” which uses agents that make it possible to mix asphalt at lower heats, dramatically cutting the amount of energy needed to produce it and the greenhouse gas emissions released.
But researchers are going beyond these relatively simple improvements by developing other materials entirely: smarter pavements that come with lower environmental impacts. Several states are beginning to use permeable pavements that allow water to seep through; a new sidewalk in Cambridge will use permeable concrete along with a “rain garden” catchment system to keep polluted storm water from draining to the Charles River. Researchers are even developing pavements that filter impurities from the water that passes through them. A team at Eindhoven University of Technology in the Netherlands have developed a kind of concrete that purifies the air above it by sucking up nitrogen oxides. Other engineers are investigating asphalts made from plant biomass, and concrete made from industrial waste products.
Massachusetts drivers are all too familiar with another weakness of old-fashioned street materials: the ways extreme seasonal temperatures make road surfaces expand and contract, which causes them to ripple, crack, and collapse into potholes. Rajib Mallick, a civil engineer at Worcester Polytechnic Institute, is developing road surfaces that don’t reach extreme temperatures, to prevent rutting in the summer and cracking in the winter, while also reducing the “heat island effect” that paved surfaces cause. What he is trying to design, in other words, is a road that protects itself from the costly, near-constant rebuilding that plagues every American municipality where roads freeze and thaw. The approach involves using a layer of heat-conducting, flexible material below the surface of a road, which would direct heat into the surrounding soil, where it can more easily disperse.
And that might be just the beginning of a revolution in what roads do for us. Ideally, Mallick says, that conducted heat could someday be trapped and used for energy. With roads, he says, “you have millions of miles open to the sun.” Right now we pour energy into transportation; a bigger question, he says, is “how can we utilize the transportation network as a source of energy?” If we could find a way to transform those inert miles of asphalt into the equivalent of solar panels, the enormous highway system where we burn so much fuel could actually begin to give something back.
ENVIRONMENTALISTS AND URBAN planners dream of a country less reliant on automobiles; so do people who have survived serious car accidents, or anyone who’s watched their money tick away into the gas tank. But while cheaper and more environmentally friendly methods of transportation exist — bicycles, public transportation, small electric vehicles — transportation planners have struggled to entice people to give up their cars. Part of this is because of roads themselves. As much as they open up the landscape and allow us to live and work in far-flung places, they also lock us into certain ways of getting around.
So what if redesigning roads could open up new transportation possibilities? Ian Lockwood, a transportation engineer currently on a Loeb fellowship at Harvard, explains that after World War II, engineers tried to reduce congestion and boost the speed and efficiency of driving on major roads by making them wider, straighter, and faster — which causes development to spread out and makes us more dependent on our cars. Many cities are now reversing course, undergoing “road diets” to cut back lanes, and trying to revamp roads to encourage walking and biking.
This is simply a change in planning; no major additional resources are required. But Mark Delucchi, a transportation researcher at University of California Davis, is considering more expansive, imaginative fixes. Delucchi says that one reason people are reluctant to use smaller, less energy-intensive vehicles is that for now, they have to share the road with heavy, fast-moving SUVs. But what if there were a safe course on which to drive personal vehicles that require less energy per person — not just a bicycle or moped, but even a souped-up golf cart or a small electric car? With this idea in mind, Delucchi has advocated a new design for towns and suburbs: two separate road systems, with the majority of local roads designed for small, slow, neighborhood vehicles, and a smaller number of roads for regular cars that connect towns and suburbs. Although no community has yet adopted a system like this, there are a few places where people have ditched their cars to take advantage of alternative road networks. The master-planned community of Peachtree City, Ga., has a 90-mile network of paths for golf carts, pedestrians, and bicycles, while the town of Houten in the Netherlands has a dedicated network of bicycle paths, with limited access for cars in the town center.
As Delucchi’s plan suggests, to truly promote new modes of transportation, we might need new kinds of roads entirely. In a recent article in the journal Solutions, Richard Forman and transportation researcher Daniel Sperling imagine a smarter road system of the future, which would replace highways in the most environmentally sensitive areas with raised roads they call “netways.” In their vision, we wouldn’t use cars at all, but electric, centrally powered personal pods that take us from place to place. These roads would be well out of reach of both wildlife and waterways. Though it’s futuristic and ambitious, Forman insists that “almost all the technologies are there.” A similar system is being piloted in the zero-energy planned city of Masdar in Abu Dhabi.
It may be a long time before we see entirely new systems of roads designed for small vehicles or pods. For now, we’re seeing gradual revisions: from car culture to multiple modes of transportation, and from asphalt blockades to crossable, energy-efficient highways. If these efforts work, we will still have roads to inspire our imagination, but we’ll draw even more rewards from their reality.