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A new study identifies the precise ways that stricter land use regulations lead to greater divides.

We’ve long known two things about land use regulations. One is that elements of them—in the form of large lot requirements and other aspects of “exclusionary zoning”—have led to the racial and economic segregation. The other is that restrictive land use and building codes in cities limit housing construction (and therefore housing supply), leading to increased costs, worse affordability problems, and deepened inequality in urban centers.

What we haven’t fully understood—until now—is how restrictive land use regulations in cities and urban centers shape segregation across entire metropolitan areas. A new study by Michael C. Lens and Paavo Monkkonen from UCLA’s Luskin School of Public Affairs*, published in the Journal of the American Planning Association, takes on the precise nature of the connection between land use restrictions and the economic segregation of metros. The study uses new and better measures for both segregation and land use restrictions to examine this relationship in 95 large metropolitan areas in 2000 and 2010.

To measure land use regulation, the study uses the Wharton Residential Land Use Regulation Index (developed by real estate economist Joseph Gyourko and his collaborators), which is based on 11 categories of land use regulation. To get at economic segregation, the study uses advanced measures from sociologists Sean Reardon of Stanford, David O’ Sullivan of Berkeley, and Kendra Bischoff of Cornell that assess not just income segregation overall, but how segregated the poor and the wealthy are across metro areas. The study employs detailed statistical models that control for the factors that influence segregation like population size, race, poverty, affluence, inequality, the number of jurisdictions, and independent of metropolitan fragmentation.

Ultimately, the research leads to four key findings that improve our understanding of the connection between land use restrictions and segregation.

1. Density restrictions isolate the wealthy

Density restrictions work to increase segregation, mainly by exacerbating the concentration of affluence. This contradicts the commonly held belief that exclusionary zoning leads to the concentration of the poor. Instead, the authors find that the main effect of density restrictions is to enable the wealthy to wall themselves off from other groups.

This result aligns with my own findings, which suggest that segregation of the wealthy, highly educated, and knowledge class is the driving force of overall economic segregation. These groups colonize the most central, economically functional, and desirable locations—in turn shunting the poor, less educated, and service and working classes.

2. Restrictions in both cities and suburbs matter

The economic segregation of metros is significantly higher in places where cities (not just suburbs) employ more stringent land use and density restrictions. This finding adds important nuance to the conventional view that segregation is the consequence of exclusionary zoning in the suburbs. Density restrictions in the city not only lead to higher housing prices (think San Francisco), but to greater economic segregation across a metro as a whole. As the authors write, “density restrictions are a culprit in the social fragmentation of metropolitan areas and should be relaxed where possible.”

3. Local government restrictions contribute to segregation

The precise way in which the government is involved in land use regulation is a key contributor to segregation. Many people assume that segregation is the consequence of exclusionary zoning, broadly speaking. But the new study finds that segregation varies by both the nature and extent of government involvement, as well as the type of land use restriction. Notably, the authors discover that segregation is not associated with a broad measure of land use restriction overall, but is instead the result of more specific types of regulation and restrictiveness.

On the one hand, segregation is positively associated with land use restrictions, such as local project approvals and local zoning approvals. Places that require multiple levels of approval to get housing built are more segregated, largely because such regulations hinder new housing development. Furthermore, segregation is higher in metros where local governments are more involved in residential development and feel pressured to restrict population growth. On the other hand, segregation is not associated with open space requirements, supply restrictions, or delayed approvals.

4. State involvement can temper segregation

Segregation is lower in cities and metros where state governments are more involved in land use regulation, residential development, and growth management.

Overall, the findings of the study have substantial implications not just for our understanding of the way urban form and land use restrictions impact economic segregation, but for urban policy as well. For one, they tell us that not all forms of land use restrictions are a problem: some (like zoning approvals) are much bigger culprits than others (like open space requirements).

The study also shows that cities and urban centers play an important role in economic segregation in addition to suburbs. Not only do restrictions on density lead to higher housing prices (as a growing chorus of urban economists have shown), they also shape economic segregation across entire metros. So strategies to reduce economic segregation must be regionally based and involve central cities as well as suburbs. Here the authors point out that “efforts to force wealthier parts of [the] city to build housing for low-income households, or inclusionary housing, are more effective at reducing segregation than bringing higher-income households into lower-income parts of the city.”

Importantly, the study shows that greater involvement at the state level can help temper some of the most damaging effects of exclusionary zoning. The authors write:

Greater pressure from multiple local interest groups regarding residential development exacerbates the tendency to segregate by income. At the same time, income segregation is ameliorated by a higher level of involvement from state institutions. Taken together, these findings suggest that land use decisions cannot be concentrated in the hands of local actors.

The complication here, of course, is that most state legislatures are controlled by suburban and rural interests and have historically shown little desire to address urban problems like segregation and inequality. Perhaps this will change as the problems of poverty, inequality, and segregation shift from their historic location in cities and urban centers to suburbs and metropolitan areas more broadly.

*CORRECTION: An earlier version of this story mistakenly referred to the Luskin School of Public Health. It is the Luskin School of Public Affairs.

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