Above photo: Aerial view of Minneapolis. Daniel McCullough / Unsplash.
A New Study Shows Just How Much.
New research shows that urban highways have weakened social ties in all of America’s 50 largest cities.
A new study confirms what urban residents and advocates have known for decades: that America’s urban highways are barriers to social connection.
The research, published this month in the journal PNAS, quantifies for the first time how highways have disrupted neighborhoods across the 50 biggest U.S. cities. Every single city studied showed less social connectivity between neighborhoods where highways are present.
“Nobody could put a number on the disruption, and now we can give a score to every single highway segment,” says Luca Aiello, a professor at the IT University of Copenhagen and the study’s lead author.
By comparing the social connections between people living on either side of highways to a baseline model of the same city with no highways, researchers found that the three U.S. cities that have experienced the most social disruption from highway infrastructure are Cleveland, Orlando and Milwaukee.
To infer individual social ties, the study relied upon geolocated user data from social media platform X (formerly Twitter). Researchers assumed that two individuals were connected if they had mutual followers and estimated users’ home location based on where their posts were sent from.
Aiello notes that there has long been “qualitative or small-scale evidence” that highways and other urban infrastructure are disruptive to local communities, especially Black neighborhoods.
“The problem is that nobody had any way to quantitatively measure how much this infrastructure impacts or decreases people’s opportunities to connect across these large highways,” he says. “If we can quantify and put a number on this, we can quantify the damage that it is doing to our social fabric.”
In all the cities studied, the barrier effect was stronger at shorter distances (less than about 3 miles) and weaker at longer distances (of about 12 miles and more). “If someone wants to cross a multi-lane highway, it takes a lot of effort,” explains co-author Anastassia Vybornova of the IT University of Copenhagen. “So highways connect over long distances, but divide over short ones.”
A long history of disruptive infrastructure
Researchers found several examples of highways as interracial barriers, where a predominantly Black community lives on one side of the highway and a predominantly white community exists on the other. Detroit’s Eight Mile Road is a classic example.
They also found examples of highways as intraracial barriers, where the highway runs directly through a predominantly Black community. Nashville’s I-40 – which split up a vibrant middle-class Black neighborhood, displacing about 80% of Nashville’s Black businesses, more than 600 homes and close to 1,500 people – is one of many such cases.
Highway infrastructure has long been connected to racial segregation practices across the United States. In 1956, President Dwight Eisenhower passed the Federal Aid Highway Act, allotting $25 billion to build 41,000 miles worth of highways.
The goal was to create a way to connect cities and address the poor road conditions. Ultimately, though, building highways through cities provided white suburbanites with convenient commutes to urban centers, while also allowing governments to remove entire communities of color in the name of “urban renewal” and “slum clearance.”
As Black Americans began migrating to cities to pursue economic opportunities, wealthier white residents left urban areas for the suburbs in a phenomenon known as “white flight.” The interests of white suburbanites — who wanted to use highways to access the city for work and entertainment, but also wanted to protect their own property values and businesses — heavily influenced infrastructure development plans.
According to the U.S. Department of Transportation, these interstates displaced more than 475,000 households and over one million people. Today, community leaders and historians alike acknowledge that highways were a key tool for segregating and displacing Black communities during the 1950s and ‘60s.
A call for policy solutions
Research has long established negative long-term health impacts for those living and working near highways. The exposure to increased air and noise pollution, particularly with 300 meters of highways, can lead to an increased risk for lung disease, heart problems, premature birth, respiratory diseases, neurological disorders and more.
But more sparse social connections have very real consequences for residents’ health and economic wellbeing, too.
“[Highways] limit social opportunities, and those social opportunities are connected directly to financial opportunities,” Aiello says. “Over time we see how these communities continue to lose.”
City governments and urban planners have increasingly begun working to mitigate these effects by removing or capping highways, with former U.S. Transportation Secretary Pete Buttigieg noting in 2021 that “there is racism physically built into some of our highways.”
Last year, the Biden administration announced $3.3 billion for projects to reconnect neighborhoods divided by the federal highway system. Funds for this program, and others with equity goals, have been halted under the Trump administration.