Jessica Trounstine: It’s true that these regulations were first used 100 years ago, but the current pattern of restrictive zoning did not really take off across the U.S. until the 1970s. Land-use regulations tend to get layered over time. Once a local government enacts land-use regulations, they don’t tend to roll them back. So over time, land-use regulations frequently get more and more exclusionary.

At the same time, population has increased in major metropolitan areas for a variety of different reasons. But housing development has slowed. The market gets squeezed over time. It is only in recent decades that we’ve really seen the confluence of all of these events, so that even the price of housing for middle-income families can be very high.

How have zoning and land-use policies contributed to racial segregation?

Jessica Trounstine: Segregation for many decades was driven predominantly by private market decisions: racial steering, blockbusting, restrictive covenants, and violence, even, to defend the color line. But those tactics became at least technically illegal in the middle of the 20th century through court cases, state laws and the federal Fair Housing Act of 1968.

Restrictive zoning essentially arose to take the place of these kinds of tactics. The U.S. is much more segregated today than it would be if it weren’t for restrictive zoning. On top of that, restrictive zoning freezes in place segregation patterns that were created by overt racist actions decades ago. We are about twice as segregated as we would otherwise be if we didn’t have these kinds of regulations in place.

What strategies can municipalities use to address housing shortages and segregation?

Jessica Trounstine: They can think about having all kinds of housing in every neighborhood – all forms of housing to appeal to different kinds of people at different income levels.

They can do things like eliminate parking minimums and expand height restrictions. Even more dramatically, they can create public funds for low-income developments.

What strategies make zoning and land-use reforms more effective?

Jessica Trounstine: No single reform can work on its own. Simply allowing duplexes to be built is frequently not enough. But we do know that packages of reforms can work together.

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