The Twin Cities’ biggest urban freeway is having a moment of serious reconsideration. Multiple advocacy groups are taking advantage of Interstate 94’s planned reconstruction to advance alternatives — with some proposing a land bridge to cap a portion of the freeway, and others proposing to replace the entire freeway with a multi-modal boulevard.
The movement to address the harms of freeways is not limited to local advocates, however. Researchers have been releasing new, rigorous research on freeways, deepening our understanding of both who they harm and how that harm plays out. Two recent studies describe how a freeway’s benefits are spatially distributed, examining the consequences of urban freeways running through populated urban areas. These studies are essential readings as we decide the future of our urban highways, both in the Twin Cities and elsewhere.
The first paper, published in 2022 by economists Jeffrey Brinkman and Jeffrey Lin, uses technical urban economic modeling to demonstrate the substantial local disamenity effects of freeways. We are already well aware of the harms that freeways introduce via air and sound pollution, as thousands of cars roar by each day while releasing carbon emissions and particulate matter. But Brinkman and Lin address how these disamenities reshaped our cities, while also focusing on a less precisely studied disamenity: how freeways act as barriers and sever the urban fabric.
Previous economic research has examined the benefits of freeways as valuable regional connectors. Researchers have found that the development of freeways helped cities grow local employment and created large economic benefits by connecting cities to each other. Urban freeways also drove steep increases in suburbanization by making it viable to live on cheap land outside of the city, which also provided reductions in housing costs.
Freeways’ benefits as regional connectors are intuitive, and have come up frequently in debates over the future of I-94. People experience firsthand how freeways provide access, especially if they live further from main city centers (of course, all of these benefits come with the giant asterisk of pollution’s externality costs).
However, Brinkman and Lin write that their new analysis of freeways “de-part[s] from the consensus among economists that freeways affect spatial structure solely by reducing transport costs,” showing that freeways also reshaped our cities by creating disamenities for center-city residents. In other words, freeways do more than just link us together.
Inequities in Freeway Harms
While previous research assumed that freeways drove suburbanization solely by making suburban life better, Brinkman and Lin find that freeways drove suburban flight by making urban life worse. Freeways can serve as connectors, but they also make it more difficult for center-city residents to access amenities and jobs in their cities, alongside other pollutive reductions in quality of life. The authors conclude that efforts to restore urban connectivity at highway corridors could provide substantial benefits.
The other recent study, published in early 2023 by researchers Geoff Boeing, Yougeng Lu and Clemens Pilgram, shows how freeways’ costs and benefits are inequitably distributed. Looking at the Los Angeles area, the authors utilize careful statistical analysis to understand who drives, where they drive and who deals with the resulting pollution.
Their findings are striking: Whiter census tracts have greater proportions of drivers, who tend to drive through more racially diverse census tracts with lower proportions of drivers. Those facing the most exposure to traffic-related pollution contribute least to its creation. And though the researchers are looking at general traffic patterns, they find that much of this effect is owed to Los Angeles’s highways.
In the authors’ graphic below, observe how red census tracts — where there is a high ratio of white commuters driving through the tract relative to white residents living in the tract — cluster along the highways.
This research holds direct relevance for the Twin Cities. In the Minnesota Reformer, I recently covered demographic maps made by Our Streets Minneapolis showing that our own urban area has more vulnerable populations concentrated along the I-94 freeway corridor. As I showed last year in Streets.mn, substantial portions of new housing development in St. Paul are built close to freeways, largely owed to “snob zoning” rules that only allow for dense housing along heavily trafficked arterial corridors. Thus, residents of most new housing are forced to deal with freeways’ consequences. And as Ava Kian recently reported at MinnPost, particle pollution levels (partially driven by vehicle traffic) have been rising in the Twin Cities, and are part of steep racial disparities in exposure to air pollution.
No single study can definitively judge large-scale infrastructure projects. As Minnesotans discuss potential futures for the urban sections of I-94, they will face challenging questions about values, priorities and politics. But in response to new information about the consequences of our freeways — how they have reshaped our cities, and who wins and loses as a result — we should adjust our city planning accordingly to achieve better, more equitable outcomes.
Photo at the top depicts anti-freeway protestors in Washington D.C., 1965. Photo courtesy of DC Public Library.