We need to move away from car dependence and towards building healthier communities
In the fractured geometry of car-dominated cities, a new study from Brown University and Columbia offers a sobering reminder that the built environment is never neutral — it shapes who we become and how we suffer. Researchers examining New York City hospital data found that neighborhoods physically severed by road infrastructure face significantly higher rates of schizophrenia-related hospitalizations, a pattern that persists across all ages and cannot be explained by air pollution alone. The culprit, it seems, is not what we breathe but what we lose: the walkable streets, the chance encounters, the informal bonds that quietly hold human minds together. In designing cities for cars, we may have been quietly designing them against ourselves.
- A new metric called the Community Severance Index reveals that roads and traffic patterns don't just divide neighborhoods geographically — they fracture the social fabric that protects mental health.
- Schizophrenia-related hospital visits are measurably higher in NYC ZIP codes where car-dependent infrastructure cuts residents off from walkable access to neighbors, services, and daily life.
- The effect holds even after controlling for air pollution, challenging the assumption that electrifying vehicles will resolve the mental health toll of car-centric urban design.
- Researchers identify the likely pathways: reduced physical activity, chronic stress around road safety, shrinking social networks, and loss of the informal support systems that help vulnerable people stay well.
- Urban planners now face a reframed mandate — redesigning streets, adding pedestrian infrastructure, and reducing vehicular dominance are being recognized not as amenities but as public mental health interventions.
- The research team is expanding the index to other major U.S. cities and launching a follow-up study on how combined exposures to heat, pollution, and isolation affect elderly mental health.
A highway running through a neighborhood does more than carry traffic — it erects an invisible wall. Families on either side drift apart. Children don't cross. Shops become unreachable on foot. The connective tissue of community quietly tears.
Researchers at Brown University and Columbia have now put numbers to that tearing. Their study, published in Environmental Epidemiology, analyzed hospital visit data across New York City ZIP codes and found that communities fragmented by car-dependent road design showed significantly higher rates of schizophrenia-related hospitalizations — across all age groups, and independent of air pollution exposure.
To capture this fragmentation, the team developed the Community Severance Index, a measure of how roads, traffic volumes, and missing pedestrian infrastructure — sidewalks, crosswalks, safe crossings — physically and socially disconnect neighborhoods. The index was developed by epidemiologist Marianthi-Anna Kioumourtzoglou, now at Brown's Center for Climate, Environment and Health, alongside colleague Jaime Benavides.
The mechanisms aren't fully mapped, but they're plausible: severed communities discourage walking, generate chronic stress around road safety, shrink social networks, and cut residents off from the informal support systems that help people remain well. Urban environments have long been associated with elevated rates of anxiety and psychosis — but this research suggests the specific design of those environments carries enormous weight.
One implication cuts against a prevailing assumption: cities investing heavily in electric vehicles as a mental health and environmental fix may be solving only part of the problem. If isolation itself — not just pollution — is driving harm, cleaner cars won't be enough. "We need to move away from car dependence and towards building healthier places and communities that bring people together instead of isolating them," Kioumourtzoglou says.
The team is now working to extend the Community Severance Index to other major U.S. cities and to study how the compounding effects of extreme heat, air pollution, and social isolation affect elderly mental health. The research is funded by the National Institute of Environmental Health Sciences and the National Institute on Aging.
A highway cuts through a neighborhood. On one side of it, families. On the other side, more families—but they might as well be living in different cities. The road is a wall. You don't walk across it. Your kids don't play with kids from the other side. The stores you need are unreachable on foot. The social fabric that holds a community together gets severed, thread by thread.
This is the kind of urban isolation that researchers at Brown University and Columbia have begun to measure and connect to something concrete: more people in those neighborhoods end up in hospitals with schizophrenia diagnoses.
The study, published in Environmental Epidemiology, examined hospital visit data across New York City ZIP codes and found that communities physically fragmented by road infrastructure and car-dependent design showed higher rates of schizophrenia-related hospitalizations. The effect held steady across all age groups and remained significant even when researchers controlled for air pollution—a factor already known to harm mental health. This was not about breathing bad air. This was about being cut off.
To measure community isolation, the research team developed what they call the Community Severance Index, a metric that accounts for how roads, traffic patterns, and missing pedestrian infrastructure—sidewalks, crosswalks, safe crossing points—physically and socially disconnect neighborhoods. The index was created by Marianthi-Anna Kioumourtzoglou, now a professor of epidemiology at Brown's Center for Climate, Environment and Health, who co-led the study alongside Jaime Benavides, an epidemiologist at Brown's School of Public Health.
Benavides describes the alternative: an environment where cars exist but don't dominate, where people can walk safely to neighbors' homes, where children play outside and adults gather to talk. That's not a fantasy. It's a design choice. And the data suggests it matters for mental health in ways we've largely overlooked.
The researchers didn't pinpoint exactly why isolation correlates with schizophrenia hospitalizations, but the mechanisms are plausible. A severed community discourages walking and physical activity. It creates psychological stress around road safety. It shrinks the number of social contacts residents can maintain. It limits access to goods, services, and the informal support networks that help people stay well. Urban living in general has been linked to higher rates of anxiety, mood disorders, and schizophrenia—but this study suggests the design of that urban environment matters enormously.
Kioumourtzoglou points to a crucial implication: many cities are betting on electrified vehicles as the solution to traffic's harms. Cleaner air, fewer emissions. But if the problem isn't just pollution but the isolation created by car-dependent infrastructure itself, then switching to electric cars won't be enough. "We need to move away from car dependence and towards building healthier places and communities that bring people together instead of isolating them," she says.
For urban planners, the prescription is becoming clearer. Reduce vehicular traffic. Build parks that are actually accessible. Stop routing highways through the middle of neighborhoods. These aren't abstract quality-of-life improvements. According to this research, they're mental health interventions. The team is now working to expand the Community Severance Index so it can be applied to other large U.S. cities, and they're launching a new study to examine how the combined effects of extreme heat, air pollution, and community isolation affect the mental health of elderly people. The work is funded by the National Institute of Environmental Health Sciences and the National Institute on Aging.
Notable Quotes
We need to move away from car dependence and towards building healthier places and communities that bring people together instead of isolating them.— Marianthi-Anna Kioumourtzoglou, professor of epidemiology at Brown University
Reducing vehicular traffic, creating more easily accessible parks, and limiting highways that cut through communities can improve collective mental wellbeing.— Jaime Benavides, epidemiologist at Brown University School of Public Health
The Hearth Conversation Another angle on the story
So you're saying that living near a highway makes you more likely to be hospitalized for schizophrenia?
Not exactly. The study found that communities physically isolated by road infrastructure show higher rates of schizophrenia-related hospital visits. It's the isolation itself—the broken social connections, the inability to walk safely to neighbors—that correlates with the hospitalizations.
But couldn't it be the noise? Or the pollution from the cars?
They controlled for air pollution. The effect remained. And while noise is certainly part of the picture, the researchers are pointing to something deeper: when a road cuts a community in half, people stop interacting. They stop walking. They stop seeing each other. That social disconnection appears to be its own risk factor.
Is this specific to schizophrenia, or does it affect other mental health conditions too?
The study looked at mood disorders, anxiety, and adjustment disorders as well. But schizophrenia showed the strongest association with community isolation. The effect was consistent across all age groups, which suggests it's not about one vulnerable population—it's about how the built environment affects mental health broadly.
What would actually fix this?
Stop designing cities around cars. Create neighborhoods where you can walk to a neighbor's house safely. Keep highways from cutting through residential areas. Build accessible parks. It sounds simple because it is—but it requires rethinking how we've built most American cities.
And if we just switch to electric cars?
You get cleaner air, which is good. But you still have the isolation. You still have the broken social fabric. The researchers are saying that's not enough.