Category Archives: Sprawl

Could suburbs be self-powering?

■ solar-roof

It’s no secret that living in the suburbs is a tad energy intensive. Low-density living practically requires owning and driving a car, which consumes a large portion of suburban households’ energy budgets. But there’s an upside to sprawl, too—plenty of space for solar panels.

Researchers in Auckland, New Zealand asked what the energy balance of the suburbs would look like if photovoltaic solar panels were widespread and how that would compare with denser urban centers. They looked at a range of dwelling densities, from a low of about 6 per acre in the outer burbs to a high of 52 per acre in the city. The researchers then imagined what would happen if solar panels were installed in every location that would be viable, typically on rooftops facing north and west (this is the southern hemisphere, after all).

In dense urban areas, the area available for solar panels was low on a per capital basis. In the suburbs, that flipped. The difference was so extreme that solar panels in dense parts of the city could only meet a fraction of the demand. But in the suburbs, there was actually an excess of electricity generated, so much so that households could own—and charge—electric cars and still not consume it all.

Now, there are some caveats to this study, namely that Auckland is a relatively sunny place despite its frequent seasonal rain showers. Solar radiation in the city is 1663 kW h/m2/y, which compares favorably with Barcelona in sunny and solar-friendly Spain, which averages 1613 kW h/m2/y. Not everywhere has the potential of those places. But those that do, particularly in the Southwestern United States, are also hotbeds of sprawl. Widespread adoption of solar power would certainly change energy budgets there.

Solar-powered suburbs wouldn’t be all green—there’s still the issue of habitat disruption and fragmentation. Yet those are concerns for solar power installations, too. There’s still strong demand for low-density living, so if we were to supplant large solar installations with solar panels with houses under them, that may not be such a bad trade-off.¹ Coupled with habitat-rich yards and parks, such developments could even be more ecologically productive than a solar plant (though still less than undeveloped land). That won’t stop some people from ragging on suburbs, but they’ll have a few less reasons to do so.

  1. I’d still like to see a direct comparison of how much less land is required for a solar installation compared with a solar-powered burb before making any final conclusions—this study didn’t go into that.

Image courtesy of John Callas


Byrd H., Ho A., Sharp B. & Kumar-Nair N. (2013). Measuring the solar potential of a city and its implications for energy policy, Energy Policy, 61 944-952. DOI:

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We all want to live in small towns, and it’s killing cities

Downtown Northfield, MN

A bunch of economists and a blogger are trying to dissect the riddle of why metropolitan population density has fallen in the United States. Robert Shiller (yes, that Robert Shiller) seems to have unknowingly kicked off the whole thing when he wrote an essay a few weeks ago in which he said housing prices have actually been pretty stable when you adjust for inflation.

Bill McBride took issue with that, essentially saying that because land is scarce in cities, the value of the land (and the homes on it) should go up. Noah Smith didn’t quite agree with McBride, arguing that changes in transportation cost—everything from automobiles to telepresence—will counter the effects of population density over time, which is why house prices should remain flat. Paul Krugman jumped in and sided with Smith, mostly, citing the issue of declining metro population density across the United States.

Then Felix Salmon, the blogger, entered the picture. He wrote a post a few days ago laying out his solution to the riddle of why metro population density is declining. Rich people, he says, are moving to the city in larger numbers, and because they can afford more space, urban population densities are either holding steady or falling. That’s been pushing less wealthy people out to the suburbs and beyond. I’m skeptical that’s the real reason.

Most of the previous decade’s growth in the U.S. happened in the exurbs, those far flung outposts on the fringes of metro areas. There, populations rose by about 5 percent, much higher than the zero to 2 percent elsewhere throughout metro areas, including low-density but closer-in suburbs. People forgoing suburbs for the exurbs—that’s a nuance of the statistic that makes me question Salmon. If people are being driven out of the city because of high rents, then the suburbs should be growing swiftly, too. But they’re not—at least not as much as the exurbs.

Rather than reacting to what the rich are doing in the city, I think it’s more the result of how most of the rest of us would like to live. The exurbs are closer, by many measures, to the small town American ideal than the city or even the suburbs. Exurbs have single-family homes, big lots, wide streets, and a nearby countryside. The city doesn’t have that, and many suburbs don’t anymore, either—as cities swell, they’re becoming indistinguishable from the city. The exurbs are the new suburbs.

Krugman tries to drive home his point, saying, “the average American lives in a quite densely populated neighborhood, with more than 5000 people per square mile.” As such, he says, “real” America isn’t a small town, but rather something like metropolitan Baltimore. By pure statistics, he’s right. But that doesn’t necessarily mean the U.S. is a country trending toward Baltimore. A statistical snapshot can’t outweigh decades of cultural legacy. Most Americans may live like Baltimoreans, but do they want to?

Our cultural tendencies suggest we don’t. As long as the American ideal is to live in a small town—which to many people¹ means big yards, small downtowns, and concomitant low population densities—then that’s where we’re heading as a nation. If cities are to succeed, maybe they need to look to small towns for inspiration. Not the low densities—it wouldn’t be much of a city, then—but the more abstract qualities that draw people to them.

  1. Not necessarily me, though that’s a post for another time.

Photo by Northfielder.

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Planet of the cities

Endless city

Science fiction is littered with planet-wide cities. Star Wars had Coruscant, Isaac Asimov’s Foundation Series had Trantor, and even Star Trek, in an alternate timeline in First Contact, saw Earth paved over by the cybernetic Borg. City-planets are both a wonder and a terror—we stand in awe of our power to change the world, but also regard that ability with fear. What if we actually did it? Hundreds of years ago, it didn’t even seem possible. But the quickening pace of population growth in the 1800s changed that, and the vast environmental changes sweeping the planet today are a stern reminder of just how powerful we are.

Of course, Earth is not in any immediate danger of becoming one conurbation, but the trend isn’t promising. Urban areas around the world are expanding at double the rate of their populations. That means every person who moves to or is born in a city will, on average, take up more space than the person before them.

And soon there will be a lot more people wanting that extra space. Urban populations are expected to swell to 5 billion in the next two decades, and according to a recent study published in the Proceedings of the National Academy of Science, cities are expected to gobble up another 460,000-plus square miles (1.2 million square kilometers). Put simply, it means that cities will occupy three times more land in 2030 than they did in 2000.

That’s a staggering amount. The results are equally astounding. The east coast of China is likely to merge into one massive city. Cities in the region spanning Lake Victoria’s north shore—an arc from Burundi to Kenya—will swell 1,900 percent in area. Urban areas along the coastal strip from Côte d’Ivoire to Nigeria will grow 920 percent. Other countries like India, Mexico, and Turkey will also experience outsize urban growth. Even developed regions like North America and Japan will have to endure massive urban expansion.

There’s a lot to be concerned about with these statistics. Urban areas that grow several-fold in a few decades won’t be happy places to live—they’ll likely be dominated by slums, or at the very least snarled with traffic and choked with pollution. The situation is even more dire for the ecosystems they’ll be displacing, which are some of the most diverse in the world. That’s because we humans prefer to live in dangerous places, places dominated by disturbances like earthquakes, volcanoes, tsunamis, and floods, processes that produce rich and diverse ecosystems. As a result, the next two decades of urban expansion will imperil nearly 140 amphibian species, more than 40 mammal species, and 25 bird species.

That doesn’t mean we should halt progress and send everyone back to the farm. Cities are still more environmentally friendly on a global scale than the alternative. No, what it means is that we need to think hard—and fast—about how we’re going to cope with the booming urban areas of the next two decades. Much of that growth is going to happen in places like Africa that haven’t had large cities historically. Nigeria, for example, is projected to have more than 400 million people in 2050. That’s more that double its present population.

Success will depend on thinking big. It’ll require “more holistic policies that integrate traditional urban sectors—transport, energy, sanitation, buildings—with land use and conservation,” the study’s authors write. A “science of the city” that others have been arguing for. Developing that science is, in my mind, the only hope we have of taming these urban beasts. The cities of the future may not be the planet-consuming behemoths of our techno-futuristic tall tales, but they’ll be beyond anything we’ve ever seen before. We’ll need a science that’s equally formidable.


Seto, K.C., Guneralp, B. & Hutyra, L.R. (2012). Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools, Proceedings of the National Academy of Sciences, 109 (40) 16088. DOI: 10.1073/pnas.1211658109

Photo by Carl Lovén.

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Seeing historical processes in road networks’ patterns

Milan, 1913

Once a road, always a road. That’s the gist of a recent paper that studied 14 different municipalities in the Groane region of Italy near Milan. In cataloging 174 years of road construction, the study’s authors discovered that nearly 90 percent of the regions 100 most vital routes today were already present in 1833.

The researchers also uncovered evidence that the layout and characteristics of road networks are indicative of the age in which they were built. This is nothing new. Take a look at any metro region surrounded by a postwar subdivision—stick straight roads of the late 19th and early 20th centuries give way to ever more writhing tangles of spaghetti. What’s new is that this study claims that top-down planning didn’t drive the changes. Rather, the researchers say Groane’s roads reflect broader societal changes, that the unique circumstances of each era—agricultural through modern—shape road networks more than central planning—or lack thereof.

To arrive at that conclusion, physicist Marc Barthélemy and his colleagues digitized roads using maps and aerial photographs from seven different dates between 1833 to 2007. They threw the resultant vectors into a geographic information system, or GIS, and then distilled primal graphs—simplified maps that show only roads (called “links” in graph theory) and intersections (“nodes”).

Between 1833 and 2007, the number of intersections grew proportionately with population. The number of intersections skyrocketed—there were only 255 in 1833 but over 5,000 in 2007—but the number of connections remained relatively constant at 2.7 on average. The number of roads also increased linearly with the number of intersections. It’s almost as if the expansion of Groane’s social network was mirrored in its transportation corridors.

How those roads interacted with each other changed through time. In the early days, many roads either intersected another mid-link—forming a T-junction—while the others simply petered out in a dead end. Main drags radiated out from town centers like spokes on a wheel. Congruent 4-cornered intersections were rare. Yet as time progressed and cities spread into the countryside, the previous radial expansion gave way to the grid. In other studies, the advent of the grid was attributed to the arrival of master planning, but here in Groane, Barthélemy and his colleagues note that urban planning was never the region’s strong suit. Groane, they write, “never witnessed any large scale planning whatsoever.”

It is because of Groane’s lack of central planning that Barthélemy and his colleagues are able to draw their conclusion, that road networks morphed not because of changes in our approach to planning but because of changes in society as a whole. In essence, they assert that changes to the network were not consciously done.

It’s not surprising, really. Roads are built to handle the traffic of their time. When navigating Cambridge’s labyrinthine streets, I’m constantly reminded that they were built for horse and carriage, not a horseless carriage. The demands of the automobile are sufficiently different from horse or foot traffic. Their greater speeds require straighter rights-of-way. Intersections need to be clear and predictable. Navigation also needs to be simplified—drivers moving at 10 miles per hour have more time to look for their next turn than those moving three times faster. The grid tackles these problems with aplomb.

Road networks are a product of the processes that created them, whether that be wagon traffic from farm fields plodding to town or taxi cabs streaming out from downtown. Discerning process from pattern is also the domain of another field—landscape ecology. Landscape ecologists sweat the details of spatial configuration to learn what ecological processes are at work. The laws of landscape ecology apply just as well in the city as they do in the natural world. The city is nothing but an anthropogenic ecosystem.

Ever since Geoffrey West and his colleagues uncovered the mathematics behind why big cities are economically successfully—but also crime ridden—it has been popular to search for formulae that describe urban processes and city development. This paper by Barthélemy and his colleagues is but the latest addition to a growing literature. By themselves, these discoveries are clever and insightful. But the interesting stuff will happen when urban planning completes the transition from an observation-based science to a mathematical one, much as ecology did in the recent past. Then we’ll have a real sense of how these models will change our understanding of cities.

Map scanned by University of Texas PCL Map Collection.


Strano, E., Nicosia, V., Latora, V., Porta, S., & Barthélemy, M. (2012). Elementary processes governing the evolution of road networks Scientific Reports, 2 DOI: 10.1038/srep00296

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For metros, two cities can be better than one

Map of photos taken in Minneapolis and St. Paul, Minnesota

Cities were, for thousands of years, distinct and easily identifiable entities. You were either in the city or in the country. Medieval cities took this to the extreme, building walls to make explicit the distinction. Johann Heinrich von Thünen systematized the idea in 1826 when he sketched a hypothetical map that, when simplified, looked like a bow-and-arrow target. The city sat in the center and was surrounded by rings of successively less valuable farmland. It was all very orderly and very German. And for a while it did a good job describing the relationship between the city and the hinterland.

Then came the railroads and automobiles that shot holes through von Thünen’s well-organized bullseye. And in places where two cities were less than a few dozen miles apart, even the boundary between the two became blurred. Today, it’s not uncommon to find metropolitan areas with two, three, even four major cities anchoring them.

Von Thunen's model of land use

Multi-city metros would seem to be a many-headed monster, riddled with contrary opinions and paralyzed by indecision. But that doesn’t alway seem to be the case. As far as labor productivity is concerned, multi-city metros—or polycentric metros, as the literature calls them—may have a distinct advantage. A study of all metropolitan areas in the United States with populations above 250,000 by Evert Meijers and Martijn Burger shows that productivity is higher in metros with more than one city. The effect is especially pronounced among smaller metro areas.

Meijers and Burger speculate that’s because smaller cities tend to have smaller problems—less traffic, lower crime rates, and so on. By splitting the problems up among a few cities, polycentric metros can host a large population without experiencing the problems of a similarly sized, monocentric metro.

But the advantages of multi-city metros diminish as the entire area’s population grows. It’s as though the larger entity needs one place to focus its efforts. So a metro area with two cities, each one-half the size of London, wouldn’t necessarily be more productive than London itself.

Multi-city metros also fall short on other critical parts of city life—cultural and leisure opportunities. Cultural outposts like opera houses and art museums benefit greatly from larger populations, which typically contain more benefactors, both wealthy and otherwise. The same goes for sports teams. Every city would like one for themselves. Say Ft. Worth wants to build an art museum. It’s probably not going to attract some donors from Dallas, who would rather see one built in their city. Chicago doesn’t have such a problem. Monocentric metros don’t have to worry about sharing.

As cities’ borders swell, multi-city urban agglomerations are probably going to be more and more common. Even within existing metropolitan areas, smaller cities could rise to prominence. Minneapolis and St. Paul, for example, have had to contend with the rise of Bloomington. The key will be for leaders to learn to work together, coordinating efforts rather than stepping on each other’s toes.


Meijers, E. (2008). Summing Small Cities Does Not Make a Large City: Polycentric Urban Regions and the Provision of Cultural, Leisure and Sports Amenities Urban Studies, 45 (11), 2323-2342 DOI: 10.1177/0042098008095870

Meijers, E., & Burger, M. (2010). Spatial structure and productivity in US metropolitan areas Environment and Planning A, 42 (6), 1383-1402 DOI: 10.1068/a42151

Map of the Twin Cities by the inimitable Eric Fischer.

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Drive a lot? Housing density may not be to blame

Chicago streets at night

Pushing high density living may seem like a good way to get people out of their cars—saving them money, curbing emissions, and reducing oil dependence—but densification may not be a silver bullet, according to one recent study. The authors dug into the National Household Transportation Survey to examine per household vehicle ownership rates, vehicle miles traveled (VMT), and fuel consumption. While the results are by no means comprehensive or conclusive, they suggest that only the steepest increases in density could reduce car usage.

This post was chosen as an Editor's Selection for ResearchBlogging.orgDespite a correlation between density and car usage, other factors seem to play more important roles. Density is responsible for a fraction of annual VMT; increasing density by 1,000 housing units per square mile—a titanic leap, given that the average household is 2.6 people—reduces VMT by just 1,171 miles, all else being equal. Since that the average one-driver household in the study tacks on 10,100 miles per year, that represents just over an 11 percent drop in annual mileage.

housing density and Vehicle Miles Traveled

If you look at the numbers another way, the case for density reducing car usage looks even more tenuous. VMT only really declines substantially at the highest housing density—over 5,000 units per square mile, or about the same as Chicago. To halve VMT of the highest mileage households, you would need to increase housing density in those areas by 20- to 100- fold.

The inflexibility of our automobile usage boils down to a few factors, with work being the most important. The more workers in a household, the more drivers, and the more drivers, the more miles. A one-driver household, as noted above, tallies 10,100 miles per year; a two-driver household racks up 18,800 miles; three drivers, 33,900; four drivers, 47,700.¹ We are, by and large, beholden to our cars because we are beholden to our jobs. After that, driving increases as a result of income (richer people drive more), number of children (more and larger cars), education (higher education means more cars), and people’s life stage (households with older children have more cars).

While higher housing density doesn’t seem to reduce VMT, it does drive down fuel consumption. Households in the 50 to 250 houses per square mile range use 1,650 gallons of fuel annually, the most of any group. Every other group uses far less fuel. In the big cities, fuel usage drops to 690 gallons per household per year.² The reason? People with the space to use pickup trucks, SUVs, and vans tend to buy them more than people who live and drive on tighter city streets—they typically drive smaller, more fuel efficient vehicles. Yet this trend could be changing as we speak. Small car purchases have been increasing across the country, and anecdotally at least, I can confirm that large pickup trucks are harder than ever to sell these days.

fuel consumption and Vehicle Miles Traveled

One of the main arguments behind higher density living is that it will reduce our carbon footprint. While density may be a better long term solution, right now the most expeditious approach is to increase fuel economy. Rebuilding neighborhoods will take decades. In that time, most people will buy at least a handful of new cars, primarily for commuting to work. It would be great if everyone had access to mass transit, but for many, mass transit isn’t just a poor option, it isn’t an option at all. Those who do travel by bus or train today may only be a job change away from having to drive. Modern life demands mobility, and few things are better at providing that than the automobile.

  1. The increase from one to two drivers probably reflects some combining of trips by couples or roommates. The sharp increase from two to three drivers is probably the result of a family’s children driving to school or work.
  2. The lone outlier is areas below 50 houses per square mile, where households use 1,200 gallons per year. They probably have fewer nearby destinations, and so stay home more often.


Brownstone, D., & Golob, T. (2009). The impact of residential density on vehicle usage and energy consumption Journal of Urban Economics, 65 (1), 91-98 DOI: 10.1016/j.jue.2008.09.002

Photo by dsearls.

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Backyard neighbors and the perils of retrofitting suburbia

Accessory dwelling unit

Sprawl, in many cases, is in the past tense. It’s already happened. Though it continues in plenty of places, it’s most problematic where it already exists. For booming regions, sprawlish suburban rings threaten to choke the central city with snarled traffic and lean tax rolls. Rather than throw their hands up in disgust and move on to a city that “gets” it, a group of planners and architects have focused on retrofitting diffuse neighborhoods and intensifying four lane boulevards. In the process, there are myriad problems to tackle, but I’d like to tackle one right now: What to do with suburban housing.

Density is suburbia’s saving grace and Achille’s heal. Who wouldn’t want to be ensconced in their own private garden? But that same dispersed living isolates people and causes many of the headaches of daily life. Sprawl retrofit really means higher density living, which also means more shops close at hand and less time behind the wheel. It’s no secret that many suburban lots would easily support another house. Slapping another behind the existing one is a simple way to double the density. It’s a common approach to sprawl retrofit, and one raised at the 19th Congress for the New Urbanism. But if erecting backyard residences solves one set of headaches, it risks inflicting more in the process.

Suburban homes were built with very specific ideals in mind. The front of the house is the public side, presenting its widest part to the street, shielding the backyard and creating a private area where people can relax in relative peace. While many early car-centric suburban houses reacted tepidly to the backyard—the best they offered were a few more windows and a back door—we soon became practiced in the art of suburbia. Large picture windows, sliding doors, four-season rooms, and covered porches quickly festooned the private side. The backyard became more than an outdoor amenity—it was a private garden to be enjoyed from the indoors, too.

Hacking a lot in two and adding a second residence could destroy one of the few things many suburban homes have going for them—a sense of privacy. The attractiveness of this feature should not be underestimated. Research suggests that open views are help ensure a feeling of privacy, even more so than actual proximity. The bad of suburbia—houses turning their backs on the street—was driven by a noble aspiration—homes embracing the yard. No one wants their view to embrace another home, no matter how beautifully designed.

And so a lynchpin of sprawl retrofit—boosting the number of houses—may be the most difficult to achieve. That’s not to say it cannot be done, but it will require careful consideration to do properly. Suburbia may be, in many ways, a consequence of bad planning, but it got one thing right—the yard. We crave green, open space, and suburban lots with suburban houses have it in spades. It may have given us too much, but we shouldn’t take it away in too much haste lest we compound the mistakes of the past.

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It’s not the yard that matters, it’s the view

Photo by faceless b.

Tell me how much you drive, and I’ll tell you where you live

I-80 and M2

Travel can be revealing. In many cases, “where” can answer as much about a person as “who.” Much of who we are is tied up in what sorts of stores we frequent, where we work, and where we go for fun. While that sounds creepy—especially given the recent furor over smartphones storing location information—city-wide travel trends can help explain a lot about where we live.

A study comparing British and American travel habits discovered that trip distances in the United States predictably lengthen as the population thins out. In Great Britain, though, that relationship isn’t as strong, in part due to its greater population density. But when the researchers filtered out differences in income and density between Great Britain and the U.S., the British still traveled less.

The reason behind the travel discrepancy, the researchers suspect, lies in the strict separation of space for living, working, and shopping that is common in the U.S. To arrive at that conclusion, they had to use a bit of mathematical cleverness to make an apples-to-apples comparison. The model compared British and American cities of similar population and density, but shuffled the contents of the American ones until their general urban form resembled their ale-swilling counterparts. This meant that shops were now next to houses, grocery stores located just down the street, and pubs scattered about town. The results suggest that the jumbled urban land uses in England, Scotland, and Wales keep the lid on travel distances.

The British also get out from behind the wheel more often, using their feet for something other than operating gas and brake pedals. Whereas under 7 percent of trips in the U.S. are taken on foot, nearly one-third are in Great Britain. And while almost 90 percent of trips in the U.S. are made by car; only 58 percent are in Britain. More people in Britain take buses and trains, too. This modal flexibility could help explain why British of different incomes tend to take similar numbers of trips, unlike in the U.S. where wealthier people step out more often. In both countries, though, wealth is still tightly correlated with mobility, which is partially reflective of people’s ability to own, maintain, and fuel automobiles for such trips.

The one odd bit the researchers discovered was that people in smaller metropolitan areas—with populations between 250,000 to 500,000—traveled more frequently than larger ones. In theory, residents of large metro areas should have more available destinations and ways to get there, which left them stumped as to why big city people made fewer trips. My suspicion? Smaller metro areas may be a sweet spot in the spectrum, with just enough destinations and modes of transportation without the congestion present in big cities.


Giuliano, G., & Narayan, D. (2003). Another look at travel patterns and urban form: The US and Great Britain Urban Studies, 40 (11), 2295-2312 DOI: 10.1080/0042098032000123303

Photos by Minesweeper and Loganberry.

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Urbanites leave the car behind, but not as often as you might think

Urbanites leave the car behind, but not as often as you might think

Night traffic in New York City

It’s generally accepted as fact that people in big cities drive less. Things are closer together there, making it easier to walk to the store for a gallon of milk. For longer trips, mass transit is also an option. But boiling all that common sense down to a single number is difficult. And though our data-happy society can overdo it at times, numbers can reveal some surprising facts that simple observations otherwise wouldn’t—like the fact that increasing density reduces the amount people have to drive, but not by as much as you might suspect.

Determining precisely how far people drive—vehicle mile travelled (VMT) in the parlance of the field—is important for a number of reasons. With it, we can gauge greenhouse gas emissions from automobiles, allocate resources for road repairs or expansions, and refocus efforts to reduce car dependency. VMT is especially important in California, where the Global Warming Solution Act (also known as AB 32) calls on the state to reduce greenhouse gas emissions by 25 percent below 1990 levels by 2020. Cities and counties without a plan to reduce emissions within their jurisdictions risk losing transportation funding. With this in mind, two researchers from the University of California, Berkeley, set out to measure VMT per person in 370 urban areas around the United States and see how the built environment affects that number.

They discovered that people in more urbanized areas do drive less, but not that much less. Their lowest estimate for VMT was based on population density, but their more realistic result, which came from a model with more parameters, shows less of a reduction. Ironically, greater density is to blame for the lower than expected drop in VMT. As population density increases, VMT drops, but the densities of roads, shops, and services rise, all of which encourage automobile trips.

Urban areas need more roads because they have more traffic, which in turn tends to encourage more traffic. The researchers call it the “Los Angeles effect.” As Los Angeles filled the San Fernando Valley, it didn’t follow central travel corridors. Rather, it oozed out like a blob. This not only hindered mass transit in the city, it also required more roads to accommodate people’s varied travel patterns. The result is a “thicket of criss-crossing freeways and major arteries that form a dense road network,” the study’s authors write. Though Los Angeles is an extreme example of the road/population density relationship, other cities suffer from the malady, too.

The second curiosity that drives VMT in cities is the density of shops and services. It’s often easier to find a wider variety of goods and services closer to home in a city, which encourages people to leave home more often. So while people in cities still drive less, they don’t drive as little as they could.


Cervero, R., & Murakami, J. (2010). Effects of built environments on vehicle miles traveled: evidence from 370 US urbanized areas Environment and Planning A, 42 (2), 400-418 DOI: 10.1068/a4236

Photo by Josh Liba.

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Tell me how much you drive, and I’ll tell you where you live

The rural-urban fringe, circa 1942

Sears House No. 115

It’s cliché to say, “Everything that’s old is new again,” but boy if it isn’t true sometimes. I recently unearthed a monograph from 1942 about the conflict between urban and rural land uses, and a number of sections read like they were written yesterday.

George Wehrwein, the author of the monograph and a well respected land economist in his time, speaks with a voice that sounds distinctly modern. He assails unguided development as “suburban slums.” He points out farmland’s unfortunate role in absorbing willy-nilly growth. He mentions the more than 2,000 cities that, even in 1942, were utterly dependent on automobiles—“these cities have no street cars or buses of any type.” Even in that austere time, the beginnings of the automobile’s coming golden age were evident.

While the automobile and the “modern highway” were accelerating the pace of suburbanization, they didn’t start the trend—streetcars and interurban lines were initially responsible. “Almost as soon as railways became established, industries began to ‘decentralize’ by seeking locations in the suburban areas,” Wehrwein writes. While both trains and automobiles drove decentralization, they invaded rural spaces in distinctly different ways. Trains left a pattern of hub-and-spoke development, drawing some industries far out of the metropolis while leaving closer yet less accessible land under the plow. Automobiles allowed this decentralization to diffuse across the landscape even further while also invading the interstitial spaces left by train-focused development. “As a result, cities have not merely expanded, they have ‘exploded,’ ” he wrote.

Cars and highways spread development more evenly across the landscape, but much of the growth came at the expense of valuable farmland, something that clearly rankled the economist. Large tracts of land weren’t developed immediately, leaving empty lots set amidst trafficless roads, both of which became financial burdens on the local government. In his paper, Wehrwein condemns speculators that drove such slapdash development and rails against weak rural governments that did little to check them. He wasn’t universally panning the suburbs, but he was dismayed at what he saw as a waste of land and resources.

If Wehrwein’s lamentations sound distinctly modern, then so too do his solutions. He calls for large scale regional planning in his paper and advocates granting counties the power to guide development in unincorporated areas. Thanks to his earlier efforts, that experiment had already begun on in a few places. Twenty-five of Wisconsin’s 72 counties had zoning laws, and the state of California granted local authorities power to do the same. But Wehrwein also realized that granting authority does not ensure a desired outcome. “Mere power does not carry with it the desire, courage, or the wisdom necessary to make for a well planned rural-urban region.”


Wehrwein, G. (1942). The Rural-Urban Fringe Economic Geography, 18 (3) DOI: 10.2307/141123

Image in the public domain.

The great (big) American lawn

A lawn being mowed

Spring is descending on the United States. Buds on trees and shrubs are swelling, and brittle brown grass is beginning to show green signs of life. As people put away their snow shovels and dust off their lawn mowers, it’s also a good time to take stock of the American lawn, which plays a starring role in the American dream. Backyard barbecues or weekend touch football games wouldn’t be the same without them, and there is something pleasing about a house perched amidst a nice green carpet. But grass is also a fussy plant, needing to be watered, fertilized, weeded, and, of course, mowed. For many, lawns are an American nightmare, yet we love them anyway.

Some Americans like to say they bleed red, white, and blue, but many should probably add green to that list, such is their devotion to their lawns. I myself am intimately acquainted with lawns and have been for many years. I started mowing my parents’ lawn as soon as I could safely see over the mower’s handle and took on a handful of my neighbors’ shortly thereafter. It didn’t take long until I was a lawn mowing connoisseur, changing the cutting pattern with every mow to give the yard a bit of golf course confidence. Even in college I couldn’t escape lawns. One of my summer jobs involved navigating a Toro Groundsmaster 322-D across school yards for eight hours a day. Even today, I still like the smell of freshly cut grass.

Our attachment to lawns means they have moved with us, even to climates where no lawn has any right to grow. Given how large they figure in the American subconscious, just how big is the collective American lawn? Nearly 50,000 square miles. That’s three times more than the area of irrigated corn in the U.S. And we grow a lot of corn. We’re still rolling out the green carpet, too. Between 1978 and 2001, we added between 170 and 355 square miles of lawn each year (depending on how you estimate it).

Much of that growth has come from the expanding suburbs. Lawns aren’t necessarily bigger than they used to be—in fact, median lot sizes have decreased while houses have continued to grow.¹ Part of the reason is that two story houses are more popular than before. Whereas only 23 percent of homes built in 1973 were had two stories, 53 percent do today.² So while houses have increased in size, lawns have kept pace, if only because they’ve reclaimed some of the built footprint.

More land under the seed-water-fertilize-mow regimen means more chemical applications, too. And given the intensity with which we dose our lawns, that should concern us. About 71 million pounds of active ingredients of herbicides, insecticides, fungicides, and other chemicals are dumped on U.S. lawns each year, or about 7 percent of all pesticides used in the U.S. Lawns may be attractive greenery, but they’re anything but green.

That’s not to say we should do away with lawns entirely. No way. But perhaps we could all do a little better by following two maxims my dad has for his lawn. First, he reasons that more fertilizer means more mowing. He applies it like a diabetic sugars his coffee—sparingly. It’s just enough to prevent our yard from becoming a neighborhood disgrace, but it’s a savvy approach. Some of our old neighbors fertilized religiously and therefore mowed religiously. The second mantra speaks to lawn size. “If the lawn takes longer than half an hour to mow, then it’s too big,” he says. While the half-hour rule was never entirely accurate—I paid close attention to how long I spent behind the mower—it’s the idea that matters. Our back yard was wreathed in butternut trees, general shrubbery, a small pond, and an honest-to-goodness prairie, all there, in part, to cut down on the amount of grass we had to maintain.  Some people might balk at giving up that much turf, but I can assure you, it was still enough for a weekend game of football with my friends.

  1. Average lot size—which is skewed by mammoth properties—has grown slightly since 1976.
  2. Fun fact: Split level homes which were all the rage in the 1970s and 1980s peaked at 12 percent of new homes in 1975 and 1976. Today, their numbers are little more than a statistical hiccup.


Fishel, Frederick M. 2011. Pesticide Use Trends in the U. S. : Pesticides for Home and Garden Uses. PI-140. University of Florida Institute of Food and Agricultural Sciences Extension.

Grube, Arthur, David Donaldson, Timothy Kiely, and La Wu. 2011. Pesticides Industry Sales and Usage: 2006 and 2007 Market Estimates. U.S. Environmental Protection Agency.

Lindsey, Rebecca. 2005. Looking for lawns. NASA Earth Observatory.

Robbins, P. (2003). Turfgrass revolution: measuring the expansion of the American lawn Land Use Policy, 20 (2), 181-194 DOI: 10.1016/S0264-8377(03)00006-1

U.S. Census Bureau. 2010. Characteristics of New Housing.

Photo by seantoyer.

Related post:

It’s not the yard that matters, it’s the view

Plants rockin’ the suburbs, animals not so much

Hidden cost of sprawl: Getting to school

The cost of getting to school

click for more detail

Chalk it up to the law of unintended consequences. As Americans have flocked to the suburbs for the lower cost of living, the cost of sending their kids to school has gone up. Where most kids used to walk to school—myself included—nowadays many simply live too far away. While some students get rides from their parents, many are left to take the bus, an option that is funded by districts. But as kids travel farther to get to school, the costs for busing them have also gone up.

Fully 56 percent of people living in metropolitan areas in 1950 resided in their region’s big city (or cities). By 2000, that proportion had dropped to 32 percent. At the same time, the cost of sending kids to school has increased from $289 per student to $737 per student.¹ It might be tempting to blame gas and diesel prices, but they aren’t responsible—they’ve remained largely constant over that time period when adjusted for inflation (except for the energy crisis in the 1970s). Yet the trend in student transportation costs has risen unabated. Though the outlay may not seem significant, it is money that would be spent more effectively in the classroom.

  1. All costs are inflation adjusted to 2007 dollars.


Boustan, Leah Platt, and Allison Shertzer. 2010. Demography and Population Loss from Central Cities, 1950-2000. California Center for Population Research Working Paper PWP-CCPR-2010-19. Available online.

U.S. Department of Education. 2009. Digest of Education Statistics. Table 147.

Are wildlife diseases cities’ next public health problem?

Raccoon chows down a pumpkin

Cities were nasty, filthy places to live until very recently. For many people in slums around the world, this remains a cruel part of life. The place that holds the most opportunity also harbors disease and illness. People have been grappling with the ill effects of population density for thousands of years, and most of the effort has focused on how to stop one person from getting another sick. But as cities’ populations boom, there’s another less considered and seemingly unlikely source of disease—wildlife.

This post was chosen as an Editor's Selection for ResearchBlogging.orgPeople and animals have a long history of trading diseases. The Black Death was caused by bubonic plague, a bacteria carried by fleas that typically infest rats and other rodents. HIV is widely believed to have first infected humans via contact with another species of ape. And though animals have given us a few beneficial diseases—cowpox, for example, which helped end smallpox—by and large, they’re something we’d rather avoid.

The collision of urban and rural areas has brought a number of diseases to our attention. Lyme disease has become a household name in much of North America thanks to expanding suburbs. As cities pushed out into old farm fields and forests, more people came into contact with the deer ticks that carry the bacteria that causes the ailment. A bite from a host tick causes a telltale bullseye rash followed by fever, headaches, and if left untreated, joint inflammation and nerve damage.

Rabies is another disease that can be problematic in cities, but unlike Lyme disease, it has a worldwide reach. Though dogs are the primary vector for humans, other canines such as raccoons provide a reservoir for the disease. As anyone who woken up to marauded garbage cans knows, raccoons are a big problem in North American cities (and in Germany, Japan, and parts of the former USSR, thanks to introductions). Raccoons thrive in human dominated landscapes: Our cities and towns are largely free of predators. They offer a variety of housing opportunities, and they come replete with buffets every night of the week—garbage night. The masked canines have made the most of it—their birth rates have skyrocketed. As their populations rise, there is more social contact and more probability for disease transmission. Nightly garbage feasts only compound this problem, bringing crowds of raccoons together. Rabies has become such a problem among raccoons that a study in Connecticut in the early 1990s discovered almost half the study population was infected.

For each common critter that is susceptible to a disease, it seems there are vulnerable species that are also threatened. Raccoon roundworm, for example, has taken its toll on the endangered Allegheny woodrat. Gray squirrels, which are not native to the United Kingdom, carry a virus which is lethal to native red squirrels. As gray and red squirrels come into contact at the same food sources in cities and suburbs, the likelihood of cross-species transmission increases. Even pets pose a threat to native fauna. Sea otters off the coast of California have come down with toxoplasmosis, the source of which was traced to urban runoff tainted with cat feces.

People once thought that cleaning up cities involved brooms, sewer systems, and potable water supplies. While those advances have gone a long way to making cities healthier, our inadvertent assistance of certain animals has raised an entirely new set of problems. Because of the wide range of diseases and hosts, the solutions will have to be varied. In the case of rabies, some areas are experimenting with oral vaccines for raccoons. But for other, more vulnerable species, the best solution may be to promote biodiversity and native landscapes. Landscapes filled with native plants would not only be less stressful for the animals—giving their immune systems a boost—they would also support more diverse fauna. A wider variety of animals within city limits would likely reduce the spread of some diseases by introducing new hosts, some of which may be better at fighting off pathogens.


BRADLEY, C., & ALTIZER, S. (2007). Urbanization and the ecology of wildlife diseases Trends in Ecology & Evolution, 22 (2), 95-102 DOI: 10.1016/j.tree.2006.11.001

Wilson ML, Bretsky PM, Cooper GH Jr, Egbertson SH, Van Kruiningen HJ, & Cartter ML (1997). Emergence of raccoon rabies in Connecticut, 1991-1994: spatial and temporal characteristics of animal infection and human contact. The American journal of tropical medicine and hygiene, 57 (4), 457-63 PMID: 9347964

Photo by clarkmaxwell.

When greenbelts fail

Leapfrog suburb in the Easy Bay, California

Parks are often preservationists’ first line of defense against sprawl. To many, they’re a win-win arrangement—less rambling development and more open space. But the same qualities that make them attractive to planners—higher property values, more recreational opportunities, and pleasing aesthetics—also draws new residents, undermining their sprawl-fighting virtues.

Greater London and the San Francisco Bay Area are good examples of the failure of greenbelts to stem outward expansion and encourage upward growth. Regional parks surrounding the core metropolitan area have become assets for communities outside the belt, attracting residents. So long as people have an expedient way to get to work, they’ll happily sacrifice proximity to work for a little patch of sunshine and greenery they can easily visit.

That’s the mechanism behind suburbs that leapfrog parks and greenbelts, according to two resource economists. They created sophisticated models that produced simplified SimCity maps that allowed them to see how parks of different sizes and shapes could change development patterns. Without parks, cities appeared as perfect circles on the map, with the highest density areas in the middle. The addition of a park, however, drew people away from downtown, creating a second locus of high-density development around it much the same way Central Park has attracted Manhattanites. But they found that if New York had an attractive space like Central Park outside of city limits, its population would be smeared across the landscape like butter on bread rather than centered on Manhattan like a dollop of ice cream. Typical parks with low perimeter-to-area ratios tend to affect development this way.

Greenbelts on the other hand have gobs of perimeter, making them easy to access for large numbers of people. The perimeter-to-area difference between classic parks and greenbelts means they have  different effects on development, at least within the confines of the paper’s model. Where classic parks spread development by acting as a second downtown, greenbelts that bound a city can hem it in. By diffusing a park’s benefits around the city rather than concentrating it in one place, greenbelts’ recreational values are typically lower than a classic park but accessible to more people. People want to live close to both open space and their jobs, so a properly configured greenbelt can boost neighborhood density between itself and downtown, limiting sprawl.

For greenbelts to be truly effective, the paper’s authors note, they must be sufficiently wide to discourage casual commuters from living outside its bounds. This is likely why greenbelts around cities like London and San Francisco have failed—they just weren’t big enough. Furthermore, while greenbelts can keep development inwardly focused, new parks within city limits can spur redevelopment of underpopulated areas. Together, they could be a powerful double whammy against sprawl.

Whatever the case, it’s clear that cities’ open-space strategies need to be well though out. Poorly planned park systems can have consequences that are not just unintended, but counterproductive.


Wu, J. (2003). The influence of public open space on urban spatial structure Journal of Environmental Economics and Management, 46 (2), 288-309 DOI: 10.1016/S0095-0696(03)00023-8

Photo by Troy Holden.

It’s not the yard that matters, it’s the view

Small yards

Americans love their privacy. Most aren’t keen on high rises or even attached condos, having been imprinted with a very specific American dream—that of a single-family house on a quarter acre lot. I’m one of them. But as populations in cities and suburbs boom, there’s simply less land to go around. The result of cramming detached homes into smaller spaces is often comical. With McMansions and McMansion, Jrs. shoulder-to-shoulder, the lots they sit on look like last year’s outfit on a six-foot sophomore.

Yet despite the potential aesthetic faux pas, many people want a single-family house. A lone house—never mind the neighbors six feet to the left and right—engenders feelings of independence and privacy. It’s self-sufficiency framed in two-by-fours. This is what planners and developers are up against as they struggle to fit more homes onto less land.

Such tight spacing of big houses has always been a bit of a mystery to me. The yards behind sardine houses are clearly more decorative than functional, so what’s the point of them? Wouldn’t everyone be happier if they lumped their token yards together? The resultant space would be magnitudes larger and more usable. But privacy would suffer. Or would it?

Maybe not. Homeowners feel just as happy and secluded in a single-family house as in a townhouse, so long as they have good views out their windows, according to one survey. The study asked homeowners in two neighboring developments—one with single-family houses and the other with townhouses—how they felt about their homes, their privacy, and their access to open space. Most people were happy, but the most satisfied were those whose views didn’t look directly onto the neighbors.

The differences between townhouse owners with views and without views were the most revealing. People with an open view were more likely to say they had enough space and privacy. Naturally, those with good views were also pleased with the way the subdivision was laid out, a trend which was echoed by owners of the detached single-family houses. The happiest people were those with homes that opened out onto undeveloped land like a flood plain or communal open space.

Given American’s penchant for privacy, I was surprised that owners of townhouses were more satisfied than owners of detached homes. The townhouses’ compact footprints may have given them an advantage. With 12.5 units per acre, the townhouse development was 2.5 times denser than the site with single-family houses. With the remaining space, the developers set aside 3.25 acres of open space. Though their motives for doing so weren’t clear—ordinances may have demanded it—it certainly had a positive effect on the way people viewed their own homes.

The market wasn’t as kind to the townhouses, however. Owners reported difficulty selling them while single-family houses in the neighboring development were selling like hotcakes. (This was during the mid-1990s.) So although people appear to be happy with attached housing once they’ve experienced it, most people crave the perceived privacy of single-family houses. Still if you’re looking for a home, it’s important to keep in mind that a grassy buffer may not be the path to happiness. What we see out our windows may have a larger effect on our sense of space and our happiness.


Day, L. (2000). Choosing a House: The Relationship between Dwelling Type, Perception of Privacy and Residential Satisfaction Journal of Planning Education and Research, 19 (3), 265-275 DOI: 10.1177/0739456X0001900305

Photo by IDuke.

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The roadless neighborhoods of Radburn, New Jersey

Munich: The Million Person Town

Englisher Garten, Munich

Millionendorf. The Million Person Town, as Müncheners happily call their city. It’s an apt description—Munich is as skilled at masking it’s size as Mexican druglords are at hiding their contraband. The place literally feels smaller than it is, thanks in part to it’s compact footprint. Munich’s sights are easily accessible without a car, and the idyllic German countryside is a short trip out of town. How did the Munich area avoid sprawl while its population boomed? Planning, in a word. Munich and its neighbors have been at it for 60 years.

Munich, by rights and means, should be a car town. Six Autobahnen feed car and truck traffic into the city’s heart, BMW’s world headquarters lie within the city limits, and it has the highest per capita income of all the major German cities. But despite its predisposition to automobiliphilia, Munich is one of the few major European cities which had its population grow more rapidly than its boundaries.

It all boils down to a few decisions Munich made when it rebuilt after World War II. With the city mostly bombed out, planners decided to restore the historical center to its pre-war appearance and layout, forgoing a car friendly grid. In the process, they hemmed in the old town with a ring road to deal with traffic. But the old Munich and the new ring road wouldn’t suffice for long. Just over a decade after the end of the war, the city’s population surged past one million as people flocked to the city from the countryside in search of jobs. Those jobs paid well, and rising affluence led to wider adoption of automobiles. Both of these trends often test the demands of traditional city planning. In most cases, city planners would have done what was easiest—expand.

Instead, Munich city planners took advantage of the newly passed Bundesbaugesetz (federal construction law) to form a city planning commission that oversaw not just urban development, but also economic, social, educational, and cultural interests. By 1963, they produced their first plan and a few years later formed an department tasked with coordinating planning activities and reaching out to research, business, industrial, and residential communities.

Though the plan saw few updates in subsequent decades, its 1988 revival renewed interest in keeping Munich’s footprint small. The relative paucity of sprawl in the Munich area is due in part to city’s desire to maintain its density. The city has encouraged redevelopment of its brownfields: As industries have vacated factories and military installations been abandoned, economic incentives helped fill the gaps with housing, business parks, and industrial parks. Munich’s well-oiled and thoroughly modern mass transit system has also kept residents moving efficiently despite the density. Plus, it’s a treat to ride—trains run frequently, the stations are clean, and the latest interiors of the latest trains benefit from stunning design. Finally, the city has placed an emphasis on open space. Parks like the Englisher Garten (pictured above) line the Isar River in the city, and substantial forest reserves surrounding the city have kept a lid on expansion.

Regional planning in Munich has been less codified, but similarly effective. Most municipalities in the metropolitan area have been a member of the regional planning association since the 1950s. Though participation is voluntary, the organization’s lengthy history has probably contributed to its success in orchestrating regional growth. While many similar metro areas in Germany and throughout Europe have expanded outwards, the Munich region has managed to direct much of its spatial growth to undeveloped enclaves.


European Environment Agency. 2006. Urban sprawl in Europe: The ignored challenge. EAA Report No. 10/2006.

Wengert, Norman. 1975. Land use planning and control in the German Federal Republic. Natural Resources Journal 15:511-528. (available online)

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Suburbia no more? Not quite yet

“What if” development ran rampant in Silicon Valley?

Suburbia no more? Not quite yet

Aerial view of a new subdivision

Travel just outside any large American city and one of the things you may notice is the number of new construction projects. Fresh, undeveloped land on the fringe of a metropolitan area is land ripe for the picking, every developers dream. The pace of suburban development, it would seem, has not slackened since it started in the 1950s. But things are not always what they seem. Though many major American cities are continuing to grow, each person they add is taking up less land than the person before them. From Houston to New York to Los Angeles, cities are consuming land at a slower rate than before.

The study that stumbled upon this nugget was originally looking for links between types of zoning laws and the amount of land consumed per additional person in a metropolitan area. They found that cities with ordinances that encouraged the redevelopment of old sites within city limits reduced their per capita land consumption by twice as much as cities with more traditional zoning laws. Overall, major metro areas in the U.S. added 1,184 square feet (110 square m) less land per person in 2000 than they had in 1990. Additionally, in cities that did slow their rate of per capita land consumption, more people settled in denser neighborhoods. The study shows that zoning laws do have an effect…sort of. It turns out that zoning laws are not entirely responsible for the change.

Part of the proof is the fact that four of the major Texas metropolitan areas grew and consumed less land per capita, too. If you’ve ever visited or flown over any of these cities—Houston, Dallas/Ft. Worth, Austin, San Antonio—you know they don’t keep a tight leash on development. I’ve visited or driven through each of them over the years, and I got the impression they were sitting atop massive suburban volcanoes, spewing strip mall magma and tract housing pyroclastics. Since Texas does not have many natural barriers to impede city growth, you’d think its cities would just keep growing. Except they haven’t.

The study’s authors don’t touch on possible reasons behind the Texas anomaly—there were too few metro areas that followed the zoning creed to make any statistical inferences—but I have hunch why their rate of per capita land consumption is dropping like a stone. Without trains to rapidly move people from place to place, the freeways and tollways have become saturated with traffic. Large, low-density cities simply take too long to traverse. People in Texas may be warming up to higher density living, but not after thousands of square miles have been gobbled up by Walmarts and Whataburgers.

The sprawling cities of the Southeast may want to take notice of what’s happening in Texas. Though many saw their per capita land consumption slow as well, their urban cores did not grow any denser, suggesting they may follow a very Texas-like trajectory. On the other side of the country, many Western cities, such as Phoenix, have already reached their saturation points and have begun to densify.

Still, not every city is building up instead of out. The Grand Forks, ND, metro area, for example, has been adding a whopping 1.3 acres (0.54 ha) per person, compared to the New York metro area, which has added only one tenth of an acre (0.05 ha) per person.

While inward-looking zoning laws have reduced the rate at which cities are expanding per person, they apparently have not had much of an impact on the proportion of people living in denser neighborhoods. What does seem to work are conservation programs. Funding for such initiatives seems to be a very strong indicator that a city is densifying. “Cities with any level of conservation funding are denser than cities with no conservation funding,” the authors report. Though they have no data to explain why this is, they do have a few reasonable guesses. It could be that the conservation money sets some land aside for parks. Or maybe people who live in cities that invest in conservation are willing to live in denser neighborhoods.

Overall, many of America’s cities are finally curbing their seemingly insatiable appetite for land, but many have a long way to go before they begin to look like New York or San Francisco. Most of the land within American cities is locked up in low density development, which houses a relatively small number of people. So long as the desire for such housing exists, cities will continue expand.


McDonald, Robert I., Richard T. T. Forman, and Peter Kareiva. 2010. Open Space Loss and Land Inequality in United States’ Cities, 1990–2000. PLoS ONE 5: e9509. DOI: 10.1371/ journal.pone.0009509

Photo by opacity.

800 million spaces and nowhere to park?

parking lot

It’s sad but true. Americans likely have 800 million parking spaces at their disposal and many of us (myself included) have driven round and round the block looking for a spot. What gives? It’s the distribution, of course. Parking availability is heavily skewed to the places that seem to need it the least, like the suburbs. If you’re in a big city, that knowledge is a maddening fact of life. But there’s more to our surfeit of spots than simple frustration. Parking represents a large and often hidden cost of driving, and according to a study that estimated the number of spots, it adds to cars’ already substantial carbon footprints.

A team of engineers from UC Berkeley assembled a virtual dossier of parking spaces across the country. They drew on data from commercial parking companies, policy reports, government databases, surveys, and the urban planner’s old rule-of-thumb—eight parking spaces per car. The authors estimate the number of spots ranges from a low of 105 million (just those reported by an industry group) to a high of 2 billion (the rule-of-thumb estimate). The middle three estimates each fell around 800 million spaces, the number on which most media reports seem to have settled as the correct guess.¹

It’s likely then that the U.S. has over 500 million more parking spaces than registered vehicles. For every 100 square meters of roadway, there is about 50 square meters of parking space. In sum, the amount of land devoted roadways and parking in the U.S. can cover the entire state of West Virginia—that’s about 24,000 square miles or 62,000 square kilometers. If we use the study’s middle of the road estimates, a third of that number—about the size of New Jersey—is solely devoted to parking. Clearly, we have too much parking space in this country. The glut of free and cheap parking artificially lowers the cost of driving, encouraging people to stay in their cars, planners to pave more land, and politicians to look unfavorably on mass transit.

Even in dense urban areas, parking is woefully underpriced, according to Donald Shoup, the “prophet of parking.” Fortunately, many cities are starting to ratchet up prices. San Francisco has even gone so far as to pilot smart meters that adjust rates based on the availability of spaces as measured by in-road wireless sensors. The goal is to leave 15 percent of spaces free at all times, a number Shoup’s research says minimizes the amount of time people hunt for parking spaces and thus reduces greenhouse gas emissions.

Smarter use of parking spaces is not the only way to limit their environmental impact. Reducing the number would also create some some drastic results. The energy and resources that go into paving for parking increases carbon emissions by 62 percent for sedans and SUVs and 67 percent for pickup trucks. Plus, associated emissions of soot and volatile organic compounds are also substantially higher, offsetting some of the benefits of catalytic converters on cars and trucks. Less land paved by asphalt would also reduce the urban heat island effect, which in turn would lessen the strain on buildings’ air conditioning systems.

The inventory’s cataloged environmental impacts, though extensive, are only part of the story. For example, the study does not calculate the additional amount of roadway and other infrastructure that is required to accommodate massive parking lots and wider streets. Many communities require wide roadways for street parking despite the fact that nearly all of their houses and apartment buildings have off-street parking. The reduction in paved areas would be substantial if these communities would build narrower roads and restrict parking to one side. City footprints would also shrink. Even in existing neighborhoods, road rebuilding projects could pare down street widths and widen parkways.² Though the amount of added greenery would seem small, a 30 percent reduction in impervious roadway surfaces would ease the strain on sewer and water treatment systems and help mitigate flooding.

To think, our cities could be radically different if we’d just reconsider the number of parking spaces we really need.

  1. Many articles on the study report the authors claim 800 million is the most likely estimate, but I couldn’t find confirmation of that anywhere in the article. Still, 2 billion seems unreasonably high, and 105 million improbably low, so 800 million is a good guess.
  2. Also known as tree lawns, sidewalk buffers, devil strips, city grass, and so on. If you need a picture, here you go.


Chester, M., Horvath, A., & Madanat, S. (2010). Parking infrastructure: energy, emissions, and automobile life-cycle environmental accounting Environmental Research Letters, 5 (3) DOI: 10.1088/1748-9326/5/3/034001

Photo by Troy Holden.

O megalopolis, megalopolis! Wherefore art thou, megalopolis?

BosWash megalopolis

Twenty some years ago when I was leafing through my fourth grade social studies textbook, I became absolutely captivated by the idea of a megalopolis. “BosWash” was the one that really stuck in my head. The idea of one continuous city stretching from Boston to Washington, D.C. seemed unfathomable. Hell, downtown Milwaukee seemed big to me. But one city, stretching for hundreds of miles. It’s the sort of big thinking that grabs a nine year old and doesn’t let go.

Well it’s been twenty years, and I haven’t heard much about megalopolises in that time. If these agglomerations were really going to be the way many of us were to live, why haven’t we heard more about them? “BosWash” and “SanSac” have failed to enter the vernacular, though the Northeast or Northern California have continued to grow. So what happened to megalopolises? My hunch? They never went away—they merely became reality. Plain, boring reality.

BosWash and other megalopolises do not look like what a fourth grader would imagine a continuous city to be. They’re not a line of skyscrapers hundreds of miles long, or even a stream of townhouses and four-story office buildings. Instead, they’re just cities and suburbs stretching farther than the eye can see. My disappointment upon discovering the reality of megalopolises is not unlike to my reaction at learning the Pacific garbage gyre was not, in fact, an dense, walkable island of plastic the size of Texas.

Megalopolises and the Pacific garbage gyre have a lot more in common than just my own disillusionment. Both are larger than life, stirring our sense of awe (even if that awe is for how wantonly wasteful we are). Their realities are the sort that could never live up to our imaginations. Both are continuous, but also no where near as dense as we (or I) had imagined. BosWash is still five distinct major cities lodged in a matrix of smaller cities and suburbs. It sure feels continuous traveling between them, but it’s not all asphalt jungle between Boston and D.C.

Though megalopolises have slowly become reality, the word and the concept have been around for while. The original Megalopolis was an ancient Greek city smack in the middle of the Peloponnesian peninsula. It was a large city for the time (the Wikipedia article on the place mentions, not once but twice, that it had a theater that sat 20,000). Use of the term, especially as it pertains to large modern cities, didn’t become widespread until the early 1800s. The Oxford English Dictionary cites Webster’s American Dictionary as the first source of the word in 1828, meaning it had probably been a part of the lexicon for a number of years (aside: reading one dictionary cite another was a very “meta” experience). In 1927, Sir Patrick Geddes, a sociologist and city planner, whipped the term into its most current definition—a “city overgrown”—and London’s Daily Telegraph appropriately applied the epithet to Los Angeles forty-two years later.

In the intervening years, geographer Jean Gottmann intensively studied the United States’ Northeast megalopolis, helping cement the idea of a region-wide city in our social psyche. Futurist Hermann Kahn would name the region BosWash in 1967, a mere ten years before my social studies textbook was most likely published. Unfortunately for Kahn, the name didn’t stick, probably because it sounds kind of silly. Moreover, it fails to capture how the region has grown. Fingers of BosWash have extended north into Maine and south into southern Virginia, according to a 2005 Virginia Tech study (pdf).¹

Back in the 1960s, the notion of cities hundreds of miles long seemed so fanciful and future-friendly that it resonated with the zeitgeist. But as I think about the term today, it seems a lot less romantic. Yes, I’m not in fourth grade any more, and no, Boston, New York, and Washington have not slipped into decay. But what joins them is not a massive, continuous city, but a string of suburbs that just sort of popped into existence, suffocating the small towns in between. The anchor cities themselves still retain their particular character, which probably made fabricated name like BosWash feel, well, fabricated. The future will almost certainly bring many more megalopolises, but I’m guessing it will take a while before people cotton to the idea of being part of one giant city rather than a locality within a booming region. Until they do, the term “megalopolis” will probably remain relegated to academia and fourth grade text books.

  1. The same study rightly tries to do away with such constructions as “BosWash” and “SanSac” because they are unused, but then insists on calling region-wide cities “megapolitans” rather than “megalopolises,” despite its own finding that the latter is far more widely used than the former. So much for going with the flow.

Photoillustration by Tim De Chant. Images from NASA/Visible Earth.

“What if” development ran rampant in Silicon Valley?

Silicon Valley

Silicon Valley exploded in every way possible following World War II, well before it was known as Silicon Valley. The population boomed, houses were thrown up, and roads slithered out from the peninsula’s main drag, the El Camino Real. But as the strip malls started to take over, locals set about preserving much of the open space that remained.

Throughout the Bay Area, over 1,500 square miles have been protected from development. Some sprawl advocates such as Robert Bruegmann have suggested the sheer volume of protected land within the Bay Area has forced suburbs far into California’s Central Valley, and that the land closer to the city centers would be better used for housing. Silicon Valley itself holds a not-insignificant 181 square miles of the Bay Area’s protected land. Detractors claim the open space has hemmed in development too much, forcing additional housing elsewhere, increasing commute times, and reducing the amount of affordable housing in the Valley.

About the Finder easter egg

Even Apple engineers were enamored with the golden hills that surround Silicon Valley.

Such criticism can be difficult to deflect without ripping up woodlands and grasslands, so a group of geographers set about asking “what if” the protected land in Silicon Valley were open to development. They created a series of maps to predict where and how much development would take place by analyzing six characteristics—slope of the terrain, presence of wetlands, distance to streams, distance to railroads, and distance to historical urban centers—that would help them determine the number of additional houses each piece of land could support.

In total, they found that 51,000 additional housing units could be added in Silicon Valley if all the parks, protected watersheds, and protected wetlands were be converted to housing. For reference, the region has 790,000 units currently. Crucially, the study’s authors estimate only around 3,400 units would be on lots small enough to be considered affordable by Bay Area standards.

Topography is the main reason few affordable units would be added to the area’s housing stock. Much of the protected area in Silicon Valley is high in the hills and on steep slopes. Due to concerns over wildfires and mudslides, housing density in these areas is restricted. Existing houses built on unprotected wetlands have also been spaced far apart. Since the Valley’s large protected tracts are either up in the hills or down in the wetlands, there is little room for additional high density (and affordable) development. Over 20,000 of the additional units, they estimate, would be single family homes on large lots, around 1.6 acres each. Real estate of that size in the Bay Area is not cheap, even by Bay Area standards. Single family homes on one acre or larger lots in San Jose list for $1.5 million.

Six and a half percent more housing units might make a bit of difference in cramped Silicon Valley, but it would also do away with the open space that makes the area both livable and attractive to many. Plus, much of the gains in affordable housing would come at the expense of parks within city limits, many of which were created give residents of the surrounding high density housing a bit of fresh air and greenery. Sounds like it was a pretty good trade-off to me. Having worked with many high school students from such neighborhoods, I know many of them never made it to the Bay Area’s large regional parks. But they did spend many hours at their local neighborhood parks.


Denning, C., Mcdonald, R., & Christensen, J. (2010). Did land protection in Silicon Valley reduce the housing stock? Biological Conservation, 143 (5), 1087-1093 DOI: 10.1016/j.biocon.2010.01.025

Photo by calwhiz.