Fall 2005

How Far To The Nearest Road?

To analyze how close land in the continental United States is to roads, Riitters and Wickham used four maps showing landcover, roads, watersheds, and ecoregions. They converted the road map to a road-distance grid and then laid this grid over the other three maps.

Their results showed that:

• 20 percent of all land area was located within 400 feet of the nearest road
• 50 percent was within 1,250 feet of the nearest road
• Only 18 percent of U.S. land area was more than 3,200 feet (0.6 mile) from a road
• Only 3 percent was more than 3.1 miles from a road
• The total length of roads exceeded the total length of streams by about 600,000 miles
• Overall, forestland was slightly more remote from roads than other landcover types, but the trend was similar.

“Imagine that all the land in the United States is divided into parcels the size of a baseball diamond infield,” says Riitters. “In the continental United States, you would have 8.6 billion of these parcels. Imagine that you are standing on home plate of one of these parcels. According to our model, in one out of every 22 cases, there would be a road no farther away from you than second base. In one in five cases, the road is no farther away than the center field fence. The effects of roads on water drainage patterns, plant and animal habitat, and wildlife movement extend hundreds of feet from the roads themselves. Standing on your imaginary baseball diamond, you start to get an idea of the pervasive impacts of roads on forest ecosystems in the United States.”

Riitters and Wickham concluded that regions with more than 60 percent of their total land within 500 feet of a road may be at the greatest risk for long-range ecological impacts from roads. In the United States, these regions include nearly all coastal zones and large parts of the southeastern Coastal Plains and river basins.

For More Information:
Kurt Riitters at 919–549–4015 or kriitters@fs.fed.us