Suburbs also have less transit than urban areas, making it difficult for low-income residents to get to jobs or buy groceries. And social services have been slow to follow the poor to the suburbs, so many suburban poor find themselves isolated and without a safety net, hidden from those who might be able to help.

This all became extremely clear to the Reverend Harriet Bradley, who lives in an extended-stay motel in Gwinnett County, where a neon sign advertises rooms for $169 a week. She has no car, and depends on public transit to get around. It can take her three hours to get to church some days, and the public transit in the county doesn’t run on the weekends.

She says she was called by God to talk to other public-transit riders about the need to expand the bus system, and recently decided to attend a public hearing of the Gwinnett County Board of Commissioners to ask them to divert more support to public transit in the county. After two long bus rides, she waited through hours of dull zoning appeals and then, right before the meeting ended, was given a few minutes to speak.

The crowd was diverse, but the commissioners were all white. Over the last decade, Gwinnett has become the most racially-diverse county in Atlanta. Between the 2000 and 2010 census, the county's African American population added 112,000 residents, growing 143 percent, while the county's Asian population doubled, adding 43,000 residents. The white population grew by a mere 1,680 residents. Still, the Gwinnett County Board of Commissioners is all white, as is the county school board, and all of the judges elected to county's state and superior courts.

Bradley, who is African American, cleared her throat and stood in front of a round table of white elected officials and staff, and asked for more transit funding.

"The bus schedules don’t start early or run late enough," she said. "I’ve often heard people around me say, 'They don’t realize that I can’t get to work.'"

A person without a car who wanted to attend that very meeting would not have been able to get home afterward because the bus doesn’t run late enough, she said (she’d arranged for a ride home). Gwinnett County residents without cars can’t get jobs at the mall or local warehouses, or at Atlanta’s airport south of the city—the busiest airport in the world—because the buses don’t allow them to get to work on time.

“Many people have had to turn down jobs because they couldn’t get there,” she said, ending her speech.

Afterwards, she spoke individually to a few commissioners but felt mostly ignored. “The commissioners—they don’t really want public transportation out here,” she told me afterwards. “They wouldn’t use it anyway.”

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There are a few reasons poverty is becoming so concentrated in the suburbs, according to Berube and Kneebone. One has to do with where it’s possible to find affordable housing. After all, many suburbs were built decades ago as developers tried to offer up more spacious locations for growing families after World War II. As those homes age, the middle-class families who once lived in them leave in search of nicer, newer places being built either in farther suburbs, or in rehabilitated downtowns. More than 80 percent of units in some now lower-income suburbs like Penn Hills outside of Pittsburgh, or Webster Groves outside St. Louis were built before 1970, Kneebone says.