Defined as communities located on urban fringes where housing density is low, population growth is high and at least 20 percent of workers commute to jobs in an urban area, "exurbs" are booming throughout the United States, and especially across the South. Located where outer suburbia bumps into rural towns, exurbia sits at the cutting edge of local debates on growth and development -- and also plays a growing role in shifting national politics.

Some 5 million people live in the South's exurban areas, accounting for about 47 percent of the total exurban population nationwide, according to a new study from the Brookings Institution titled "Finding Exurbia." The states with the largest proportion of exurbanites are South Carolina, Oklahoma, Tennessee and Maryland, with Texas having the largest total number of exurban residents.

The Brookings researchers set out to discover who exactly the exurbanites are:

They are more likely to: be non-Hispanic white; live in a "nuclear" family; face daily "super-commutes" of an hour or more each way; work in construction or manufacturing; and vote Republican.

How Republican? In 2004, 63 percent of votes cast in exurban counties for either of the two major-party presidential candidates went to George W. Bush -- the mirror image of urban counties, where John Kerry won about 63 percent of the vote.

But there are indications the GOP's grip on exurbia may be loosening. In an article on exurban politics published last year in the conservative magazine The Weekly Standard, Fred Barnes pointed to the 2005 governor's race in Virginia, where Republican candidate Jerry Kilgore lost Loudoun and Prince William counties, exurbs that Bush won easily in 2004.

That trend away from lockstep Republicanism in exurban Virginia was also manifest in last week's midterm elections, where winning Democratic U.S. Senate candidate James Webb won Prince William and Loudoun counties by a slim margin -- jurisdictions that losing incumbent Republican Sen. George Allen carried in 2000.

The exurban trend toward Democrats could also be seen in House races, CQ Weekly observes:

On the House side, voters in 19 of the 28 districts where the Democrats had confirmed takeaways at the end of Election Week had, just two years ago, favored Bush over Democratic presidential challenger John Kerry. Those districts -- many of them regarded as securely Republican entering this midterm campaign year -- were strung from eastern New Hampshire to the Central Valley of California, and included seats in upstate New York, the South, the interior Midwest and the fast-growing Mountain West state of Arizona.

Most of those districts have substantial rural territory. Others are mainly in suburbs and exurbs. What both groupings have in common is that Democrats had been lagging behind Republicans.

In its report, Brookings notes that the exurbs defy certain stereotypes. That fact could put their future political role up for grabs. The exurbs are not generally destinations for "high income homeowners living in super-sized new mansions," Brookings observes. "In many metropolitan areas ... the growth of exurbs may be related to middle-income families' 'drive to qualify' for more affordable new homes that are in limited supply elsewhere."

As the war on the middle class rages on, it wouldn't be surprising if the exurbs continued to shift away from a GOP whose policies favor the wealthy and corporate interests at the expense of ordinary Americans.