Species and Sprawl: A Road Runs Through It

Species and Sprawl: Humans

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Take the once pristine Chesapeake Bay, its shores not 80 km from Mayhew’s townhouse. Despite recovery efforts, the estuary remains severely polluted from its rapidly suburbanizing watershed. Sewage-treatment wastewater and fertilizer runoff prompt algal blooms that suffocate fish and blue crabs. Eroded sediment smothers oysters and blocks sun from vegetation. Chemicals from pavement runoff and vehicle and power plant emissions are proving toxic to the bay’s 3,000 species of plants and animals.

Developing on or near wetlands like the Chesapeake Bay is also changing the hydrologic cycle. When soil is topped by pavement or buildings, precipitation can no longer accumulate in wetland reservoirs or percolate gradually to underground aquifers. Instead, it runs off impervious surfaces haphazardly, bringing floods and pollution to both wild and metropolitan areas.

Decreased Mobility

Today, 6.4 million km of public roads link our homes, businesses, and parking lots. In fact, sprawl could not exist without vehicles. In historic communities, businesses, stores, and services were within a walkable distance from residences. But Mayhew, for example, must walk 1.2 km—and back—to get a quart of milk. In 1960, 12.1 percent of Americans took public transportation to work, and 9.9 percent walked. Today, 4.7 percent use public transport, and 2.9 percent walk.

Ironically, the proliferation of roads, compounded with ineffective zoning and rapid, as-needed planning, has actually made it harder for people to get around. We drive farther, more frequently, and for longer periods than we used to. Research confirms Mayhew’s experience; in 1999, Washington, D.C., residents were driving 77 percent more than they were 1982. Nearly all the increase was due to sprawl and not simply population growth.

An Unhealthy Environment

Sprawl is also compromising human health. Motor vehicle exhaust contains carbon monoxide, smog precursors benzene and formaldehyde, and soot and other particles that are toxic to drivers and people living and working in airflow distance from well-trafficked roads. Recent sprawl studies are revealing surprising health connections, like the fact that children living near high-traffic roadways are more likely to be hospitalized for asthma and six times more likely to develop cancer. A recent report also found that increases in ozone levels from car, industry, and power-plant pollution were associated with increases in death rates in populous U.S. cities.

Choosing to drive versus walking or biking is also contributing to the nation’s obesity epidemic. A recent study in the American Journal of Health Promotion discovered that people living in sprawling communities are more likely to be overweight and have high blood pressure.

Smart Growth

The day-to-day realities of sprawl and the scores of statistics that measure its effects are encouraging some humans to reverse the trend. Community planners nationwide are espousing policies of smart growth, a widely touted brake to accelerated sprawl. Smart growth favors creating neighborhoods with a combination of housing types, communities with services and stores in easy reach of homes, a multitude of clean and efficient transportation options, and preserved open space and critical ecological areas. Effectively implementing smart growth and fostering a more natural, navigable, and survivable habitat for all species, is perhaps one of Homo sapiens’ toughest environmental challenges.