Opinion: It's time to start thinking of urban sprawl as a public health problem

A basic concept in epidemiology is the sufficient-component cause model.

Introduced by Ken Rothman in 1976, the concept notes that most diseases do not have a single causal factor, but rather have multiple factors resulting in a state of disease.

In this framework, a sufficient cause is one that inevitably produces disease; in practice, this usually only takes place in combination with several factors working together, forming components of a larger, singular cause. This is often visualized as a pie chart, with the disease as the pie and the slices as the components. For example, even in the case of COVID-19, exposure to the virus alone does not always result in infection; to guarantee catching the virus, several factors must also be present, which could include poor ventilation indoors, failure to wear a face mask, failure to be vaccinated for the disease, and a weakened immune system from stress.

The same model can be applied to non-infectious health events, such as injuries sustained from a fall. In a more recent article co-authored by Rothman, he uses the example of a broken hip resulting from a fall. A confluence of factors, including disrupted equilibrium from a prior head injury, shoes with worn-out soles, a gust of wind and the lack of a handrail, while insufficient on their own to result in the fall, in combination created circumstances to generate the fall that broke the hip.

I have often wondered about the applicability of this model beyond individual disease and toward more inanimate and collective matters, which have health implications of their own. Could this cause-component model be applied to local political issues such as housing and transportation?

Let’s say, hypothetically, there is a University of Iowa second-year student named Erica, who has just moved into her first off-campus apartment in the northside neighborhood of Iowa City. At first, this is great — she can walk or bicycle most places and dispense with a car, eliminating the costs of parking, maintenance, fuel and insurance from her expenses, not to mention the pollution a vehicle would generate.

But issues soon start to mount. A lot of people want to live on the northside, but the city downzoned the area in the 1980s, meaning that housing supply has not kept up with demand, increasing the rent on an admittedly mediocre apartment. She got a part-time job at the Olive Garden in Coralville, but the bus runs irregularly on an indirect route, making what would be a 15-minute drive an almost hour-long commute both ways.

More: Those nondescript split-level apartment buildings of Iowa City do reflect our history

So she frequently catches rides with her friend Mr. Peanutbutter, who tells her he has a much better deal on a place in North Liberty. Erica likes being able to walk to the farmers’ market on summer weekends, but she likes not spending six-plus hours on the bus every week even more.

So by her senior year, she has bid adieu to the walkable grid of Iowa City in favor of a car and the sprawl of North Liberty. A single person making this decision has a fairly limited impact on the built environment, but the cumulative effect of this decision multiplied thousands of times over has greatly aggravated urban sprawl in Johnson County. This has been borne out in Census data from 2020, which has shown that not only has Iowa City grown far more slowly than the surrounding suburbs in the last decade, it has also underperformed both the county average and prior estimates.

Erica’s decision to contribute to urban sprawl was not a result of any single factor, but rather the combination of many — expensive housing, an automobile-dependent transportation system, the hidden costs of sprawl not yet appearing on the new tract home development where she lives in North Liberty — some of which had antecedents decades before she was born.

Similarly, the causes of those aforementioned factors have their own components as well. The high cost of housing is not only a matter of limited supply of private housing brought upon by restrictive zoning, it is also from a lack of social housing, land being used for parking instead of housing, and the unique demand for housing in college towns.

Previously: What if Iowa City devoted less space to parking cars, more for housing people?

Automobile dependency stems not only from transportation planning that does not prioritize transit capacity or speeds, but also arises from a limited bicycle network, an abundance of free parking hiding the true costs of driving, a street design manual that is hostile to all forms of transportation besides driving, zoning that places residences and work far away from each other, and the price premiums placed upon walkable neighborhoods, precisely because of their scarcity in the United States. It was not just one single factor that led her to pack up and move to the suburbs, but rather some or all of them working in conjunction to favor sprawl and driving.

More than just a diatribe on urban aesthetics, the public health implications of automobile-dependent urban sprawl are fairly well-documented. Policy positions from the American Public Health Association note that current patterns of automobile-dependent sprawl result in significant adverse impacts to collective health, including traffic injuries and fatalities, reduced physical activity, exposure to air pollution, and contributions to climate change, resulting in tens of thousands of preventable deaths and billions of dollars in chronic care costs annually. The association’s recommended action steps — including discontinuing auto-centric methods of planning and development, greater investment in transit and bicycle infrastructure, and prioritization of compact development integrated with bicycle, pedestrian and public transit infrastructure — also place a high emphasis on equity, especially given the disproportionate impact of air pollution and traffic injury among racial and ethnic minorities.

Much of the writing on housing and transportation issues, even if only for the purpose of clickbait, tends to focus on single issues as a sufficient cause for the maladies the United States faces on these matters — it’s fares! It’s parking! It’s supply and demand! It’s public housing! It’s the auto lobby!

And while all of these are true to an extent, the notion that the “cause” of these issues — sprawl, high housing costs, automobile dependency — consists of several factors also suggests that effectively solving these issues will require multiple approaches. Perhaps looking at these matters from the lens of health — and the consequences to our collective well-being if substantive action does not take place — can be a starting point.

Austin Wu grew up in Cedar Rapids and is a graduate of the University of Iowa College of Public Health. In his spare time he has taken interest in local history and urban design, and through this column seeks to imagine a better tangible future in eastern Iowa by taking inspiration from principles of the past. It will appear in the Press-Citizen twice monthly. Follow him on Twitter, @theaustinwu.

This article originally appeared on Iowa City Press-Citizen: Opinion: Start thinking of urban sprawl as a public health problem