As environmental hazards go, few can match the toll of roads.

It’s well known, for instance, that roads — particularly new ones —open up land to suburban growth, which runs over nature with homes, driveways, strip malls, and convenience stores. That’s why efforts so far to minimize the damage that sprawl can cause has focused on reducing the need for new roads with more public transit and more incentives for builders to put houses and stores in existing town centers.

But new research reveals that, even as communities cut down on the number of new highways, they can do still more to make sure roads cause the least damage possible. Mostly uncovered in the last five years, scientific studies show that roadkill is just one of many worries for wild creatures and their habitats. Roads subject animals to upwards of 20 more hazards and hardships. The findings are so compelling that traffic engineers are starting to wonder: Can’t we build roads that make way for nature?

Some states are working to answer that question. Montana and Florida lead the nation so far in efforts to plan roads around wildlife needs and habits. A typical solution, for example, is to find where deer tend to cross a particular stretch of land and then build an underpass or land bridge into the design of a new road. Both animals and humans benefit from such forward-thinking, according to longer-term experience with it in Europe. Road modifications made with nature in mind reduce car collisions with animals, support the health of local wildlife populations, and prompt additional land-use planning measures to fit human communities with the animal kingdom.

The first step to wildlife-friendly road building is to take stock of the full extent of roads’ effects on the plants and animals in their wake. The recent barrage of evidence tells the story:

Roads actually attract some animals. Deer, for instance, relish de-icing salt, and snakes love warmed asphalt, while songbirds favor gravel shoulders for dust baths.

Roads alter behavior. Many animals strive to avoid them, even if it means confinement to areas hemmed in by roads and subdivisions. Confinement can cause inbreeding and population declines. Also, just being near roads can disrupt many natural rhythms. Eagles nesting near roads are less productive. Traffic noise disturbs frogs and other critters that communicate with calls. Streetlamp light confuses nighttime-migrating songbirds and distracts moths that should be seeking mates.

Roads damage habitat. Earth movers fill wetlands, turn forest into grassland, level hills, and mash soil. Roads also cause soil erosion and fill waterways with sediment because asphalt doesn’t absorb rain. Instead it sends stormwater rushing in torrents across fragile landscapes. Road building takes out Bunyonesque swaths of trees, which eliminates food, shelter, and the river-cooling canopies of leaves that some fish need.

Roads cause pollution. Traffic raises dust that coats plant leaves and impedes photosynthesis. Road salt runoff can drastically alter the chemical balance of rivers, essentially "pickling" them while killing flora and fauna. (Canada’s environmental protection agency, in fact, has declared road salt an environmental toxin.) Roads are also avenues for toxins and petroleum products that vehicles leak. Plants absorb these poisons and then sicken animals that eat them. Road toxins also flow into waterways, causing oxygen-depleting weed growth and introducing metals and other contaminants to the food chain.

Roads pave the way for undesirables. Vehicles transport non-native plants and pests that can take hold and out-compete native flora and fauna that sustain wildlife. Predators come, too, such as crows, which capitalize on the convenience of forest-penetrating stretches of highway to raid normally inaccessible bird nests.

These findings shouldn’t be surprising, really, according to just-retired Florida Department of Transportation ecologist Gary Evink, who’s been sounding the alarm for 20 years about the devastating effects roads have on wildlife. "Environmental considerations are not included early enough in the planning process," he explains. But a surge of interest nationwide encourages Mr. Evink. "I believe we can have wildlife-friendly roads."

Some states are beginning to build road modifications, such as species-specific wildlife crossings. Transit workers in Florida have built a natural landscape land bridge over one interstate to reconnect an open space that animals use to move from one place to another. Florida also has worked to determine where and how to build underpasses that animals will actually use. As part of its work, Florida has created a process that helps road planners consider less-destructive options. And in Montana, construction of a new highway now includes wildlife crossings in corridors that animals travel.

Scientists and engineers also are coming together to share wildlife-friendly road ideas thanks to the International Conference on Wildlife Ecology and Transportation, held annually since 1997. Last summer at the conference, a group of U.S. transportation officials and activists studied wildlife-accommodating measures in Europe, where wildlife concerns have been incorporated into road building and maintenance for years now.

"In Europe, road work on existing alignments has been a catalyst to improve not only the highway situation but land management and protection around the highway," says Mr. Evink. "This is the direction we need to move."

Meanwhile, new campaigns by the Defenders of Wildlife, the Humane Society, and Federal Highway Administration have begun raising public awareness. "Roadkill is the number one form of mortality for certain species," such as the ocelot and Florida panther, notes Trish White of Defenders of Wildlife. "The trouble is, ecology requires animals to move around," she says. "Roads get in the way." Woodland-dwelling salamanders, for instance, migrate to seasonal wetlands to mate. Black bears forage at the same spots, but only during springtime. The good news is that road builders can do something about it by taking steps to keep habitat continuous and keep road-induced sprawl and pollution from cornering nature.

Joe Bower is an environmental journalist based in Kalamazoo, Michigan. He is reachable at joebower@chartermi.net