Beyond the suburbs, yet apart from the countryside, is a familiar realm with a less-than-familiar name: the exurbs.

According to a new report from the Brookings Institution, the exurbs are a crucible of change in the U.S. landscape, and the Chesapeake Bay watershed contains many of them.

The exurbs also influence the quality of life—and environment—for the entire metropolitan region to which they belong. “What we do with exurbia will have a disproportionate impact on the future shape of the metropolitan area,” said Alan Berube, lead researcher and co-author of the report.

Exurban communities exist at the outer fringe of a metropolitan area. They are less developed than the suburbs, but no longer truly rural, with increasing ties to the urban center. Exurbs are towns and counties with an agricultural heritage, now bursting with large-lot subdivisions, a growing population of “super-commuters,” and a slate of difficult questions about schools, roads, land preservation and community character.

The Brookings report, titled “Finding Exurbia: American’s Fast-Growing Communities at the Metropolitan Fringe,” outlines the elements that define exurbia and maps where they exist.

It reinforces conclusions of a recent Bay Program analysis that found exurban areas had some of the highest growth rates in the Chesapeake watershed. A recent report, “The State of the Chesapeake Forests,” warned that the low-density sprawl associated with exurban development can accelerate the loss of valuable forests within the watershed.

The Brookings study found the percentage of exurban population in many parts the Chesapeake Bay watershed is above the national average.

“The greater Washington-Baltimore area is one of the focal points for exurbia in the United States today,” Berube said. “When you look around the watershed you see exurbs on all sides—on the eastern and western shores of the Bay, to the far south of D.C., to the north bleeding into Pennsylvania, and west into the Shenandoah and West Virginia.”

Maryland ranks among the four states with the highest percentage of exurbanites, while Virginia and Pennsylvania fall among the top 12. Ranked by absolute numbers, the Washington, D.C. metropolitan area is in the top three.

Nationwide, the population in exurbia remains low. The exurbs are home to 4 percent of the general population and 6 percent of those in metropolitan areas.

But their numbers are growing quickly—at more than twice the rate of their more urban neighbors, with a median rise of 31.4 percent in the 1990s alone.

Some exurbs may become tomorrow’s suburbs, increasing job opportunities but sacrificing the qualities that drew people to them in the first place.

“If the exurbs continue to develop, they will become places of employment as well as places of residence, but many will shed the rural character that defined them 20 or 30 years ago,” Berube said.

But sustaining exurban development patterns has costs, too. Large-lot development consumes forests and farmland, and strains community resources. Resisting denser development may push sprawl farther into the countryside.

“If the exurbs maintain a low-density, residence-only character, the fact of the matter is that the development will go somewhere else,” Berube said. “Indications are that it will go farther out, and to places beyond the exurbs. The potential for more traffic congestion and loss of rural land go with it.”

Vulnerable farmland, forests, and waterways will also be affected.

“As we develop more land in places like Hagerstown and St. Mary’s County, we lessen the quality of life in the region,” Berube said. “We lose some of the things people value, like untrampled land.”

Decisions about minimum lot sizes, locations of schools and transportation investments will play a large role in how exurbia evolves. Berube emphasized that maintaining quality of life throughout the region will also require looking at areas closer to the urban core.

“Development in the exurbs is consuming so much land that, if it continues unabated, it will really change the shape and character of the larger area in ways that development closer to the urban core, or along recognized transportation routes, may not,” Berube said. “We could tap into more resources in the cities and inner suburbs for redevelopment, and we need relief from the policies or lack of foresight that block it.”

The mutual influence of urban and exurban development decisions makes sense, given that “Finding Exurbia” defines the exurbs by their connections to an urban center, rather than their distance from it. The connections may be social, cultural or economic.

At least 20 percent of exurbanites travel to jobs in the urban or suburban core, and roughly half work outside of their home county. Many are “super commuters,” who rise early and commute at least one hour in each direction. Little to no public transportation is available, so most drive their own cars—and there is no evidence that exurbanites telecommute more than their urban or suburban neighbors. Construction, farming and manufacturing create the bulk of the local job base.

Exurbanites tend to be non-Hispanic white, middle-income homeowners. While some exurbs have evolved into upscale enclaves, others draw newcomers because the homes are more affordable than in the suburbs.

Still others come for a semi-rural lifestyle, with access to lakes, forests and mountains. In these “recreation exurbs,” seasonal homes have been converted to year-round residences, and new homes are joining them.

Politically, the exurbs are heavily Republican. Exurban voters drew attention in the 2004 presidential election, but Berube said the exurbs will not be important swing votes unless they begin a clear transition to suburbs.

“Politically, the importance of the exurbs has been a little bit overstated,” Berube said. “They still represent a small proportion of nation. The political action seems to be in the next ring, in emerging suburbs like Loudon (VA) County, Prince William (VA) County and Howard (MD) County.”

But exurban votes will still play a role in choosing local leaders, who will in turn shape local land use policy.

“We have to look at urban and suburban areas as development opportunities and think carefully about how these fringe areas develop,” Berube said. “That’s not to say there shouldn’t be more development in the exurbs, but it should probably occur within existing communities, instead of new ones.”

Exurbia in the Chesapeake Bay Watershed

Exurban counties are defined as those in which 1 in 5 residents lives in the exurbs

Harrisburg-Carlisle, PA Metro Area

Exurbs are home to 14.4 percent of the metropolitan population.

Exurban counties (2): Juniata and Perry

Virginia beach/Norfolk/Newport News, VA Metro Area

Exurbs are home to 6 percent of the metropolitan population.

Exurban counties (7): Gloucester, Isle of Wight, Middlesex, Suffolk City, Surry, VA. Currituck and Gates, NC

Richmond, VA Metro Area

Exurbs are home to 14 percent of the metropolitan population.

Exurban counties (11): Amelia, Caroline, Charles City, Cumberland, Goochland, Hanover, King William, Louisa, New Kent, Powhatan, and Sussex

Washington, D.C / Arlington/Alexandria VA Metro Area

Exurbs are home to 7.1 percent of the metro population.

Exurban counties (11): Calvert, Charles and Frederick, MD. Culpeper, Fauquier, King George, Orange, Spotsylvania, Stafford and Warren, VA. Jefferson, WV