Walking on a Redline: Did Discriminatory U.S. Housing Policies Affect Greenspace Development?

Nearly a century ago, a New Deal–era U.S. federal agency developed a color-coding method for mortgage lenders to evaluate the worthiness of neighborhoods across the country. The Home Owners’ Loan Corporation (HOLC) considered characteristics such as racial/ethnic makeup of neighborhoods, age and condition of housing, and access to public services when they evaluated the possible risk to lenders.1 People were systematically denied loans to buy homes or businesses in high-risk “redlined” neighborhoods, and what followed were decades of neglect and disinvestment. Even though redlining as a policy was outlawed in the late 1960s,2 it continues to have not only a social and economic impact on communities, but also an environmental health one.3 A recent study in Environmental Health Perspectives offers new data about the legacy of redlining in American cities and its relationship to greenspace development.4

This 1933 map of Birmingham, Alabama, demonstrates the color-coding system10 used by the HOLC to determine the riskiness of making loans for properties in certain neighborhoods. Wealthy White neighborhoods were marked in green and given an A (“best”) grade as the safest investments. Blue B neighborhoods were deemed “still desirable,” although less so, whereas neighborhoods with a lot of recent immigrants might get a yellow C (“declining”) grade. Low-income, ethnically diverse neighborhoods were outlined in red and rated D (“hazardous” to lenders). This particular map includes an additional designation separate from the HOLC system: solid gray for areas with a “Negro concentration.” Cross-hatching indicates industrial and commercial areas, and diagonal lines indicate undeveloped property. Image: Courtesy U.S. National Archives.

Anthony Nardone, lead author of the new study and a student in the Joint Medical Program at the University of California, Berkeley, and University of California, San Francisco, says the paper emerged from research that he and his colleagues were conducting on asthma5 and birth outcomes6 in historically redlined communities. “When we were hypothesizing the reasons as to why current outcomes are worse in these places today, one of the things that kept coming up was just the actual physical built environment,” says Nardone. In many of the historically redlined areas, the land was more often covered by impervious surfaces like asphalt and sidewalks, and the neighborhoods had a dearth of parks and trees.7

Nardone and his colleagues knew they could simply overlay the original HOLC maps with more recent satellite imagery of neighborhood vegetation, but they wanted to probe any potential associations more deeply by controlling for other sociodemographic factors, such as the racial composition of neighborhoods, median home values, and number of employed people. They mined demographic data from the 1940 U.S. Census and used machine learning to calculate multiple propensity scores to estimate the likelihood that a neighborhood would have been assigned a particular grade.

“We tried to compare groups that were similar like you would in a randomized controlled trial, where you try to take two groups that are essentially identical in every which way except for the treatment,” says Nardone. In this way, they could compare C neighborhoods that could have just as well been graded D, or B neighborhoods that might have been graded A.

The results showed that neighborhoods that had lower HOLC grades in the past tended to have fewer green resources like parks and trees in the present day. This was true even when controlling for historical demographic factors. Nardone says the results help quantify how the federal government and the banking industry were “able to use their power to funnel well-being and health-generating resources to predominantly White neighborhoods.”

That argument piques the interest of Lonnie Hannon, an associate professor of sociology at Tuskegee University who was not involved in the new study. He says this new study is useful in making a case that past discriminatory policies are still having a deleterious impact on Black communities decades later. “If we start with the premise that greenspace enhances health behavior,” he says, “this historical racism that has occurred over the years also leads to deficits in health behavior among current residents of these areas.” In other words, people with reduced access to greenspaces today are typically from the same racial/ethnic groups that experienced redlining. He concludes, “These ‘consequences of place’ manifest as poor health outcomes.”

Vivek Shandas, a professor of urban studies and planning at Portland State University who coauthored a study8 on redlining and urban heat in 2020, says that although we have long known that there is a general association between redlining and greenspace, this study offers more proof. “This paper helps us validate and more explicitly articulate the impacts of HOLC redlining policies on the presence of greenspace across these grades,” says Shandas, who was not involved in the new work. “It has the kind of systematic analysis that would help anybody make a clear case that redlining had an effect on the presence of anything green in those specific neighborhoods.”

Mixed evidence suggests associations between access to greenspace and improvements in mental health, cardiovascular health, birth outcomes, and child development.9 For Nardone, the issue of greenspace access is a key part of his other health-related research. “We know there are racial health disparities here in the United States, some quite drastic,” he says. He hopes that as policy makers see more evidence for how historical policies of discrimination contributed to these problems, they will be more willing to find solutions.