Three Cheers for Density

An Earth Day celebration of green cities

Density has gotten a bad rep because of COVID-19. Some of the places that are most vulnerable to the pandemic are large, dense cities like Madrid, Seattle, and New York City. All three of these cities have had some of the highest infection rates and death rates. The spread of COVID-19 in these cities was, in part, driven by density: more people living in an area means that there are more chances for individuals to transmit the disease to each other.

For some, this is a justification for reducing density. For example, New York Governor Andrew Cuomo called New York City’s density destructive and went so far as to say that the city “must develop an immediate plan to reduce density.”

Of course, as Matthew Yglesias joked on Twitter, “The moral of coronavirus is that we should adopt the kind of low-density living patterns associated with Asian countries like South Korea, Japan, Taiwan, and Singapore that have successfully controlled its spread.” It turns out that whether or not density is a health risk depends on much more than just density.

Attacking dense cities is nothing new. Like Governor Cuomo’s barb aimed at New York City, large cities are constantly being accused of not being environmentally friendly. Density is maligned as the cause of traffic, pollution, health hazards, and dirty streets.

But on this Earth Day, we aim to prove the opposite. We should celebrate density for its environmental benefits. Building up rather than out creates walkable environments that avoid emissions from transportation, saves more energy, and leaves more land undeveloped.

Density lowers emissions per capita

Research shows that large, dense cities produce fewer emissions per capita than smaller cities. A study of 355 US cities shows how cities are cleaner because they cluster activity close together. It takes less travel for city dwellers to get to work and to shop for groceries. For example, the analysis showed that relatively sprawling cities of Flagstaff, AZ, and Farmington NM produce 45 and 69 tons of carbon emissions per person. In comparison, large metropolitan areas and college towns had lower levels of emissions. Take New Orleans, which produced only 7.8 tons of emission per person and Louisville 7.4 tons per person.

For even more dramatic examples, consider the current COVID-19-ravaged New York City, which emitted only 2.3 tons per person of carbon, Los Angeles 1.8 tons, and Seattle 2.2 tons, just to mention a few. This analysis is only one of many showing the environmental benefits of density.

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Source: CityLab, 2012.

Another study found that denser forms of urban living were associated with a smaller per capita carbon footprint, for example, along the Pacific coast and North Atlantic coastal areas of the US–exactly where large cities like Boston, New York City, and Los Angeles are located. The highest carbon footprints per capita were found in the Midwest and the South, where cities are smaller and less dense.

One study from researchers at the University of California, Berkeley, provides striking visual evidence of the environmental benefits of dense cities. The study analyzes population levels and emissions by zip code. As shown in the green areas of the figure below, dense cities emit fewer greenhouse gas emissions per person, but low-density suburbs eliminate those benefits by producing more emissions.

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Source: CoolClimate Maps, derived from a 2013 study.

When we zoom into one particular city, we can see how drastic the changes are between emissions in dense urban centers and suburbs. The figure below focuses on New York City and its surrounding suburbs. Manhattan, Brooklyn, Queens, the Bronx, and parts of New Jersey — the densest parts of the metropolitan region and the ones best connected by public transit — produce the fewest emissions per household. Yet the further away you get from the downtown area and into the suburbs, the emissions per household increase.

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Source: CoolClimate Maps, derived from a 2013 study.

Cities and density evolve along with transportation options

Why are emissions per capita lower as density increases? One main reason is that people in dense cities have alternatives to cars for transportation. As density increases, car ownership, and usage declines. Density, instead, is associated with public transit, walkability, and alternative modes of transportation.

To understand this point, take a trip through history. Previously, cities could only expand as far as people could walk. As pointed out in the book Planet of Cities, new transportation technologies at the end of the 18th Century — trains and ferries — allowed cities to expand further than people could walk.

The real revolution, however, was the car. Cars meant that people could live even further away and commute to work. This made it possible for cities to disperse and spread 24 or 30 miles out of downtown.

The benefits of this expansion allowed people to live in bigger houses and larger plots of lands. But expansion also came with a downside. In suburbs, smaller towns, or even midsize cities, not having a car can make it a challenge to get around. In sprawling areas, houses take up more of the land, and amenities tend to be spread farther apart. This requires people to travel longer distances by car. In the suburbs, getting groceries, going to the movies, and going out to eat all tend to require a car.

In denser places, you could walk, bike, or take the subway to the grocery store or the movies. Cars aren’t required by design. In fact, Berkeley’s study showed that traveling to and from the suburbs is the dominant source of household carbon emissions. And the suburbs themselves account for 50 percent of all household carbon emissions in the US. Denser living enables a life without cars. Research shows that travel times tend to be shorter and can be substituted by walking or transit systems in denser settings.

This greener living also shows up in gasoline use. In his book, Green Metropolis, author and journalist David Owen points out how New York residents use less gasoline than people in other states. In especially dispersed places, like Wyoming, gasoline usage is much higher. Someone driving in Manhattan goes only a few miles when they drive at all.

Why don’t we have denser cities? Or even just denser suburbs?

Despite the environmental benefits of dense cities, land use regulations have made it hard for cities to get dense. And that’s an understatement. In many cities, zoning regulations have outlawed denser living options throughout most of their jurisdiction. Regulations tend to allow only one form of development in residential areas: single-family housing.

In 2019, reporters Emily Badger and Quoctrung Bui plotted the permitted housing developments in nine metropolitan areas. Only two of the nine, New York City and Washington, DC, allow other types of housing in more than 50 percent of their territory. The other seven range from reserving 70 percent to 94 percent of the city for only single-family homes.

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Source: New York Times, 2019.

These seven cities are not unusual. In fact, the real outliers of this study are New York and DC. As California state senator, Scott Wiener, regularly quips, zoning for single-family houses “means that everything else is banned.” And that’s the problem. Cities have bet the house on single-family zoning. And along with the environmental costs, it carries staggering economic costs.

Single-family housing is not the only way cities have limited density. Even though cities like New York are seen as dense and allow more development than single-family housing, density is restricted in other ways. A famous study published in the New York Times shows how 40 percent of Manhattan could not be built today under the current land-use regulations. Most buildings in today’s Manhattan do not conform to current zoning laws because they are too tall, have too many units, have too much commercial density, or cover up too much of the lot. The figure below shows all of the buildings in Manhattan that could not be built today.

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Source: New York Times, 2016.

Zoning regulations slow the economy in addition to harming the environment

Rules placing stringent limits on developments, like the common single-family zoning, drive up the cost of housing. In turn, high costs make it harder for people to live and work in productive cities that are clusters of opportunity. A fundamental finding in the economic study of cities is that greater numbers of people allows greater specialization. The more specialized people are, the greater the gains from trade.

To see the intuition here, think about Robinson Crusoe. Shipwrecked and alone, Crusoe has to make everything that he wants and needs by himself. His situation improves when Friday arrives, and they can begin to cooperate and trade. The trade between even just two people makes them both better off.

That story plays out at scale in huge cities with millions of people. But it’s limited by high housing costs, which plague productive cities like Los Angeles, San Francisco, and New York.

In a groundbreaking paper, economists Chang-Tai Hsieh and Enrico Moretti layout just how zoning regulations have made the US much poorer. Before Hsieh and Moretti’s work was published, researchers had shown how zoning regulations raised housing costs. The contribution that Hsieh and Moretti make is to analyze how those higher housing costs make workers less productive by reducing gains from trade. Higher rents mean that people decide to move elsewhere in the economy, for example, by taking a lower-paying job outside of an expensive city because it pays more relative to local housing costs.

Hsieh and Moretti find that zoning regulations have reduced total US growth by 36 percent between 1964 and 2009. To put that in rough but relatable terms think about it like this: if zoning rules in major cities were less restrictive, for every three dollars in your pocket, you’d have a fourth.

The alternative world that Hsieh and Moretti develop in their economic modeling isn’t a world without zoning, so change can be gradual. In fact, cities across the country are realizing the high environmental and economic costs of zoning. One city, Minneapolis, is making exactly those adjustments.

A greener and stronger future comes in twos and threes

In October of 2019, Minneapolis reformed its single-family zoning rules with the Minneapolis 2040 plan. The plan included multiple policy changes, but the crowning achievement was its tweak to single-family zoning. The changes allowed duplexes and triplexes in all areas where single-family homes were allowed.

The change can be reported in dramatic ways, though that belies its mundanity. For example, in some ways, this change triples the housing supply in much of Minneapolis. Yet, it does so without highrises or apartment buildings. In fact, it represents a return to a denser age.

Minneapolis’s changes are a return to a more resilient way of living. As Strong Towns, a housing reform nonprofit, pointed out, Minneapolis used to allow these kinds of developments. Pointing to the Whittier neighborhood, they point out that, “This type of development was made illegal in many areas in the late 20th century, and would be allowed again under the 2040 plan.”

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Source: Strong Towns, 2018.

Changes like those that Minneapolis has pursued are exactly the environmental and economic medicine needed to make cities across the US greener. Inspired in part by Minneapolis, Oregon’s lawmakers took the policy one step further and removed barriers to duplexes across the entire state. These are promising changes that will make housing more affordable while reducing their emissions.

Our land-use rules should allow diverse forms of living. Some hate the dense city, others prefer it. Yet our current zoning rules prohibit most forms of even slightly denser development. Our reliance on single-family zoning sets a single acceptable form of housing, and we pay both the economic and the environmental price for those restrictions.

On this Earth Day, let’s do what’s right for the environment and economy. It’s time to legalize housing by removing regulations that keep cities from growing up rather than out.

CGO scholars and fellows frequently comment on a variety of topics for the popular press. The views expressed therein are those of the authors and do not necessarily reflect the views of the Center for Growth and Opportunity or the views of Utah State University.