It was hoped that Housing Choice Vouchers, previously called “Section 8,” would break up dense concentrations of poverty by subsidizing rents for poor families. But the program has fallen far short of its promise. By and large, voucher holders are not moving to areas of opportunity. They are not finding places to rent in neighborhoods that include a mix of higher-income people, the kind of move shown in recent research by Harvard economist Raj Chetty and others to have long-term positive impacts on health and economic well-being. Rather, voucher holders are now concentrated in poor neighborhoods. This is even more the case for black voucher holders, whose neighborhoods are far more segregated than those of white voucher holders. Why are these patterns of segregation being recreated under a system that was meant to undo them?

A big part of the answer lies in a middleman: the landlord. Landlords play a key role in where people find homes. Yet their role in sorting residents in and out of neighborhoods remains largely unseen.

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In Baltimore, where you live has everything to do with the color of your skin. I learned this firsthand in 2011, when I was a graduate student beginning research on neighborhoods with high poverty and racial segregation, and moved into just such an area.

To begin my own housing search, I called a number on a Craigslist ad for a one-bedroom in Park Heights, a neighborhood in the northwest part of the city, and the landlord on the other end of the line asked me skeptically if I was sure I knew where Park Heights was. I convinced him to show me the converted row home later that afternoon. When I showed up, the landlord, an Air Force retiree with a head of thick, silvery hair, took one look at me and simply said, “Sweetheart, this is not a neighborhood for a girl like you.” What he meant was that this is not a neighborhood for white people. One thing was eminently clear to me even at this early stage: Landlords have enormous power to affect where people live.

I ended up spending more than a year in Park Heights, getting to know landlords and watching them show properties, do repairs, paint and repaint walls, and unclog toilets. Residents in Park Heights, as in many other neighborhoods to which voucher holders are flocking, face unimaginable poverty and violence. Life expectancy is almost 15 years lower than in affluent, white areas of the city. One in four households lives under the federal poverty line, compared to only one in six nationwide. Unemployment is rampant. Despite the drastic drop in crime across the country, the crime spike of the 1980s and 90s has only marginally abated in neighborhoods such as this one. On the day after the riots following the death of Freddie Gray a couple months ago, a man was murdered in Park Heights in an unrelated incident—the city’s 69th murder this year.