The housing market is in tatters, and house prices continue to fall precipitously in many parts of the country, so it might seem a strange time to bring up the subject of housing affordability. But one of the reasons we are in this mess is that people bought houses they couldn't really afford. At some point in the future, consumer confidence will be restored and people will start buying houses again. ­Pent-­up demand, and the inevitable delays in ­re­starting an industry that has seen the withdrawal of many home builders, will likely produce a spike in prices, and once again the affordability issue will come to the ­fore.

The term “affordable housing” has come to be associated with social programs and government subsidies, but it once meant commercially built houses that ordinary working people could afford. A pioneer of affordability was the builder Levitt and Sons, whose famous “Levittowns” were the first postwar examples of large, ­master-­planned communities. The story is ­well ­known. After World War II, as GIs came home and the peacetime economy gathered steam, the demand for housing grew dramatically. Levitt, an established Long Island builder, set its sights on this new market. William Levitt, the eldest son, applied his wartime experience building barracks with the Navy Seabees to traditional ­wood-­frame construction. He organized the building site like an assembly line. Teams of workers performed repetitive tasks, one team laying floor slabs, another erecting framing, another applying siding, and so on. No one had ever built housing that way ­before.

The first Levittown was on Long Island, the second in Bucks County, Pennsylvania, and the third in New Jersey. The Long Island project, because it was the ­first—­and the closest to New York ­City—­is the best known, but the Bucks County development, which began in 1951, was larger and more comprehensively planned and designed. At that site, the more than 17,000 homes on nearly 6,000 acres were intended chiefly for workers employed at a nearby steel plant. The largest and most expensive of the six model homes, the Country Clubber, was for supervisors and executives, but the ­three-­bedroom Levittowner was the workhorse of the development. It sold for $9,900, which would equal $82,000 today.

The term “affordable housing” has come to be associated with social programs and government subsidies, but it once meant commercially built houses that ordinary working people could afford. A pioneer of affordability was the builder Levitt and Sons, whose famous “Levittowns” were the first postwar examples of large, ­master-­planned communities.

The design of the Levittowner, like the planning of the community, was the responsibility of William’s younger brother, Alfred. Though William Levitt went on to have a long and ­well-­publicized career as a developer and builder, Alfred, who died in 1966 (at only 54), is less remembered. He was a ­self-­taught architect who had spent an entire summer observing the construction of one of Frank Lloyd Wright’s ­so-­called Usonian houses, in Great Neck Estates, Long Island. Many of the Levittowner’s ­cost-­saving features were influenced by this experience: the efficient ­one-­story plan that combined an ­eat-­in kitchen with the living room; the concrete floor slab without a basement; the ­under-­floor heating; the low, spreading roof with no attic; and the carport instead of a garage. (The Usonians, Wright’s answer to affordability, were beautiful, but since they were built one at a time, they were ­expensive—­the Rebhuhn Residence, the one Alfred studied, cost a whopping $35,000 to build in 1937, the equivalent of more than half a million dollars today.)

Many of the design innovations of the Levittowner were Alfred’s own ideas. A folding basswood screen that slid on a metal track separated a ­so-­called study-bedroom from the living room, allowing the space to be open or closed. Thermopane (insulated glass) covered a large section of the ­living-­room wall overlooking the garden. The kitchen had a large window facing the ­street—­an early example of a “picture window.” High window sills in the bedrooms provided ­privacy—­and reduced cost. Locating the bathroom and the kitchen on the street side reduced the length of piping to the street mains. There was no mechanical room; instead, a specially designed furnace fit under the kitchen counter, its warm top doubling as a hot plate. The Levitts were careful to give ­penny-­pinching buyers of the Levittowner touches of luxury: the purchase price included a kitchen exhaust fan, an electric range, a GE refrigerator, and a Bendix washing machine. The Country Clubber added a clothes ­dryer.

A ­two-­way fireplace was located between the kitchen and the living room. Two-way fireplaces were a standard Usonian feature, but while the Levittowner had a low, spreading roof and clean lines, no one would mistake it for a Frank Lloyd Wright house. Yet, although Alfred Levitt’s design looks unremarkable today, in fact this early example of the ­so-­called ranch house represented a revolution in domestic design. ­One-­story living was new to most Americans, as was the open plan combining kitchen, eating space, and living room. The undecorated exterior was unabashedly modern. Picture windows had no precedents in traditional homes; neither did carports. Instead of brick or wood, the exterior walls of the Levittowner were covered with striated sheets of Colorbestos (asbestos cement), which had been developed especially for the Levitts by the Johns Manville Corporation. With integral color that didn't require painting, this was an early example of ­low-­maintenance ­siding.

We don’t use asbestos cement anymore, and some of the other novelties, such as ­under-­floor heating, proved troublesome (as they did in the Usonians), but the Levitt brothers’ achievement remains impressive. They introduced the American public to modern production building and proved that standardization, mass production, and technical innovation could be ­successfully—­and ­profitably—­used by commercial builders to produce houses for a large market. Moreover, unlike many architectural experiments that have been dealt with harshly by the passage of ­time—­the ­high-­rise public-housing projects of the 1960s come to mind—Levittowns have remained desirable places to live. Even the names of the house models have survived. “Fabulous expanded Levittowner,” reads a recent Internet real estate ad for a house in the Bucks County community, “3 bedrooms, one bath, custom ­eat-­in kitchen.” It’s listed as ­sold.

The continuing popularity of the Levittowner after more than half a century does not mean that the demands of home buyers haven’t changed over time. Builders found out long ago that buyers would pay the small extra cost for the additional space provided by a basement. ­One-­story houses are still popular, especially with older owners, but ­two-­story houses have come back into vogue. So have traditional features such as porches, dormers, shutters, and bay windows. (The spare look of Alfred Levitt’s design would be a hard sell today.) Finally, buyers of the Levittowner were not given any choices; although Colorbestos came in seven colors, and the precise location of the carport varied from one house to another, these alternatives were predetermined by Alfred Levitt to create variety on the street. But modern buyers expect to personalize their homes. In response, while today’s builders still sell ­pre­designed models, they also offer scores of options: alternative façades, different materials, a variety of interior finishes, and “extras” such as upgraded kitchens, higher ceilings, and ­add-­on sun ­rooms.

Would it be possible to build a modern version of the affordable Levittowner? It would probably be a small house, closer to the 1,000 square feet of Alfred Levitt’s design than the 2,469 square feet that is today’s national average for new houses. Building smaller houses not only reduces construction costs, it is also good for the environment, saving materials and ­energy—­and land. The house would still have three bedrooms, but it would also have at least ­one ­and ­a ­half bathrooms, since people have come to expect a powder room, even in small houses. Closets would be bigger, and there would be more of them. There would probably not be a living room, but the house would include a family room facing the backyard. The kitchen would be larger, the ­hot-­plate furnace would be replaced by a conventional model, and the fireplace would be ­optional.

What would such a house sell for? In 1951, the price of the original Levittowner ($9,900) was three times the national average annual wage ($3,300). In 2008, with an estimated national average wage of $40,500, a similarly affordable house should have a sticker price of $121,500. Yet according to the Census Bureau, even in the current declining market the median price for a new ­single-­family house in the first quarter of 2008 approached twice that: $234,100. So, the price of a modern Levittowner would have to be nearly 50 percent cheaper than that of today’s average new house. Easy, you say, just make the house 50 percent smaller, about 1,200 instead of 2,469 square feet. But it’s not that simple. In most metropolitan areas, the selling price of such a house would still be more than $200,000, considerably more than $121,500.

So what’s keeping housing prices high? It’s not the size, and it’s not the construction costs, either. The Levittowner cost $4–$5 per square foot to build in 1951, equivalent to $30–$40 per square foot in 2008. That is approximately what an efficient, ­large-­scale production builder spends today. Home builders have followed the Levitts’ lead in streamlining construction, introducing ­labor-­saving techniques, and using industrialized materials. Plans are rationalized to reduce waste. Components arrive on the building site pre-cut and pre-assembled so that the entire construction process for a typical house takes as little as three months. Perhaps the most important change in home building concerns scale. Since the 1980s, the industry has come to be dominated by a dozen national builders. These publicly owned companies, the largest of which produces as many as 50,000 houses a year, are able to take advantage of economies of scale that the Levitts could only dream about. Large, efficient enterprises buy materials in bulk, optimize ­mass ­production of building components such as windows and doors, and operate their own prefabrication factories. This keeps construction costs ­low.

In 1951, the price of the original Levittowner ($9,900) was three times the national average annual wage ($3,300). In 2008, with an estimated national average wage of $40,500, a similarly affordable house should have a sticker price of $121,500. Yet according to the Census Bureau, even in the current declining market the median price for a new ­single-­family house in the first quarter of 2008 approached twice that: $234,100.

What’s driving the high cost of houses today is not increased construction costs or higher profits (the Levitts made $1,000 on the sale of each house), but the cost of serviced land, which is much greater than in 1951. There are two reasons for this increase. The first is Proposition 13, the 1978 California ballot initiative that required local governments to reduce property taxes and limit future increases, and sparked similar ­taxpayer-­driven initiatives in other states. Henceforth, municipalities were unable to finance the ­up-­front costs of infrastructure in new communities, as they had previously done, and instead required developers to pay for roads and sewers, and often for parks and other public amenities as well. These costs were passed on to home buyers, drastically increasing the selling price of a house.

It is a vicious circle. Smaller houses on smaller lots are the logical solution to the problem of affordability, yet ­density—­and less affluent ­neighbors—­are precisely what most communities fear most.

The other reason that serviced lots cost more is that there are fewer of them than the market demands. This is a result of widespread resistance to growth, the infamous not-in-my-backyard phenomenon, which is strongest in the Northeast, California, and the Northwest. Communities in growing metropolitan areas contend with increased urbanization, encroachment on open space, more neighbors, more traffic, and more ­school-­age children. Roads have to be widened, traffic lights added, and schools expanded, all of which lead to higher taxes. Voters commonly respond to these ill effects of growth by demanding restrictions on the number of new houses that can be built. Usually this is achieved by tightening zoning, invoking environmental constraints, and generally ­drawing ­out and complicating the permit process. It is no coincidence that house prices are highest in the Northeast, California, and the Northwest. According to the research of economists Edward Glaeser of Harvard and Joseph Gyourko of the Wharton School, since 1970 the difficulty of getting regulatory approval to build new homes is the chief cause of increases in new house prices. In other words, while demand for new houses has been growing, the number of new houses that can actually be built has been ­shrinking.

The most common tactic communities use to restrict development is to zone for large lots. In many parts of the country, the median size of new lots now exceeds one acre; by contrast, the 70-by-100-foot Levittowner lot covered less than ­one-­sixth of an acre. For the neighbors, requiring large lots has two advantages: It limits the numbers of houses that can be built and, since large lots are more expensive, it ensures that new houses will cost more, which drives up surrounding property values. But reducing development has another, less happy effect: It pushes growth even farther out, thus increasing sprawl. While ­large-­lot zoning is often done in the name of preserving open space and fighting sprawl, in fact it has the opposite ­effect.

It is a vicious circle. Smaller houses on smaller lots are the logical solution to the problem of affordability, yet ­density—­and less affluent ­neighbors—­are precisely what most communities fear most. In the name of fighting sprawl, local zoning boards enact regulations that either require larger lots or restrict development, or both. These strategies decrease the ­supply—­hence, increase the ­cost—­of developable land. Since builders pass the cost of lots on to buyers, they justify the higher land prices by building larger and more expensive houses—McMansions. This produces more community resistance, and calls for yet more restrictive regulations. In the process, housing affordability becomes an even more distant ­chimera.

 is Martin and Margie Meyerson Professor of Urbanism at the University of Pennsylvania. His latest book,

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One explanation of America's housing market collapse is that too many people bought too much house. The solution: build more affordable houses. Here's what stands in the way. 

Why Can't We Build An Affordable House?

 published what it called a global cities index, a list of 65 world cities ranked according to a variety of economic, cultural, and social indicators. Compiled by the consulting firm A. T. Kearney and the Chicago Council on Global Affairs, the index measures business activity, the size of capital markets, and the flow of goods through airports and ports. It also takes into account cultural and information resources such as the number of performance venues, the extent of broadband access, international coverage in the local press, the degree of political engagement as measured by the number of think tanks and conferences, and university enrollment and education levels. The 2010 list predictably included global powerhouses and national capitals such as London, Paris, and Tokyo, but the United States had no less than six cities in the top 20—New York, Chicago, and Los Angeles (in the top 10), as well as San Francisco, Washington, and Boston.

Lists such as these have become commonplace, and American cities are often among the top ranked. It is hardly surprising that the United States contains so many leading global cities; after all, it is an economic superpower and a very large country. What is striking is that these cities are physically so different—large as well as small, old as well as new, horizontal as well as vertical, and sprawling as well as concentrated. Clearly there is no one-size-fits-all American urban template.

Consider New York, Los Angeles, and Washington. The popular image of New York, the oldest of the three, is of a small island crammed with skyscrapers. The reality is different. Manhattan is at the heart of a metropolitan region that stretches over parts of three states, more than 3,000 square miles of cities, suburbs, and small towns. Even within the five boroughs there is considerable variety between, say, Queens, where homeownership is the norm, and Manhattan, where a majority of residents are tenants.

Compared to New York, Los Angeles is very new; 100 years ago the city had barely 100,000 inhabitants. Metropolitan Los Angeles has a reputation as a sprawling, spread-out place, yet its urbanized area is half the size of New York’s. The Angeleno city fathers have worked hard to create a distinct downtown—with limited success so far—and Los Angeles continues to be a city of many subcenters (in that sense, at least, it resembles London). Unlike London, Los Angeles is not a walkable city, yet it is dense, with mile upon mile of cheek-by-jowl dingbats, boxy two- and three-story apartment buildings.

Washington resembles neither Los Angeles nor New York. Although there are tall buildings in Rosslyn, Virginia, just across the Potomac, downtown Washington has no high buildings at all, thanks to the District of Columbia’s roughly 10-story height limit. Historically, many American cities had height limits—Los Angeles as late as 1957. The difference is that in Washington, thanks to congressional inertia, the height restriction has persisted, making Washington look more Parisian than American. The skyline consists of civic landmarks rather than skyscrapers—the Washington Monument standing in for the Eiffel Tower—and downtown is dominated by bulky office and apartment buildings. This mid-rise pattern extends quite far toward the periphery, instead of dropping off quickly to single-family houses, as it does in most American cities.

What about the other top-rated cities? Chicago’s downtown Loop is as clearly defined as Manhattan—and similarly vertical—but the flat midwestern topography has allowed the urbanized area to extend unchecked in three directions—north, south, and especially west, far past O’Hare Airport. As a result, Chicago covers a larger area than any of the other six leading American cities except New York. The historic center of Boston is compact and walkable, and although there are some skyscrapers, there is no memorable skyline. On the other hand, metropolitan Boston spreads out more than either Los Angeles or Houston. Of the six global American cities, San Francisco is the outlier; not just the hilliest city, it is also the smallest in area. Hemmed in by water on three sides (as Oakland is contained by mountains), metropolitan San Francisco is less than a third the area of Boston, and packs in more inhabitants per square mile than any of the six global cities.

For that great analyst of urban life, Jane Jacobs, density was a critical measure of a city’s vitality. Indeed, density affects the energy of streets and other public spaces, as well as the variety of amenities a city can support. In addition, density dictates the type of mass transit that is viable—buses, streetcars, light rail, or subways. Yet density is not always what it appears to be. Los Angeles, somewhat counterintuitively, is extremely dense. So are San Francisco and New York. Chicago is somewhere in between; Washington, given its height restriction—and the low density of its suburban fringe—is further down the list, although denser than either sprawling Chicago or Boston, a small city surrounded by extremely low-density suburbs.

Of course, the gross density of an entire urbanized region is a crude measure. Boston (low gross density) and San Francisco (high gross density) both have walkable, high-energy centers and a relatively large number of downtown residents. The low and compact historic cities of Georgetown and Alexandria in the D.C. metropolitan area also have high residential densities, and the highest employment density is in the capital’s mid-rise center, not Virginia’s thriving Rosslyn-Ballston corridor or the outlying edge city of Tysons Corner, as one might expect. Although Los Angeles has a high gross density, its small downtown has only half as many residents as Chicago’s. And of the six major cities, Los Angeles has the lowest share of workers using mass transit, since, unlike New York, Washington, and San Francisco, it lacks sufficiently high concentrations of people living within walking distance of transit stops.

The role of mass transit in cities is a reminder that urban density affects sustainability. It has been estimated that a Manhattanite’s carbon footprint is a third smaller than that of the average American. Dense urbanization conserves resources in many ways: Urban buildings, whether apartments or row houses, are more compact and energy efficient; amenities are concentrated, which encourages walking; and public transit becomes an option. But even the densest American urban regions are not very dense compared to those of Europe. Greater Paris, for example, covers only about 1,000 square miles, and has a gross density of 10,000 inhabitants per square mile. Greater London, confined to 600 square miles, is even denser, with about 12,850 inhabitants per square mile. And the density of Asian cities such as Singapore is even higher than that. By comparison, the gross density of a typical American urbanized area is about 2,500 inhabitants per square mile.

There are a number of ways in which American cities could become denser. In vertical downtowns, tall buildings could simply get taller, or older office towers could be converted to residential use, as has happened in some business districts. The most common form of urban densification is the conversion of disused waterfronts, decommissioned Navy yards, and obsolete industrial areas into housing and office developments, an attractive strategy since it does not displace existing residents. In older city neighborhoods, taller structures could progressively replace three- or four-story row houses and low apartment buildings, though community resistance makes this a slow process.

Suburban densification is more challenging. In Philadelphia, where I live, it was common practice in the mid-20th century to subdivide large suburban estates into communities of single-family houses, but such open spaces in the suburbs are increasingly rare. Neighborhoods of single-family housing can be made denser by building clusters of smaller houses on what were previously large single-house lots, or by introducing row houses or low-rise apartment buildings. Both strategies involve radical changes to neighborhood identity, however. Perhaps the greatest challenge will be to increase density in the large planned-unit communities that have proliferated in the past few decades. In these, any change is constrained by homeowner associations in which even a small minority of members can effectively block alterations they find objectionable.

But after a century of spreading out, will Americans change their minds and draw together? Some observers maintain (hope) that the current economic recession will encourage (force) home buyers to demand smaller homes and more densely planned communities. This result would be unusual, since previous recessions have not had similar effects. Consumers generally have short memories. Following the energy crisis of 1973, for example, Americans switched to smaller cars, but by 1984, when prices at the pump had dropped, gas-guzzling minivans appeared, soon to be followed by SUVs. In any case, choosing where one lives has never been a strictly economic proposition. It is always a trade-off among the affordability of housing, the length of commutes, the quality of neighborhood amenities—especially schools—and preferred lifestyles.

During the last decade, proponents of downtown living pointed to an increase in downtown residential construction as a harbinger of an urban renaissance, but empty condominiums in cities such as Miami and Chicago suggest that this boom was a product of the housing bubble rather than a signal of a significant change in home buyers’ preferences. Similarly, the fact that the average size of new suburban houses—and lots—has recently shrunk for the first time in decades may be less meaningful than it is made out to be. In a recession, the only customers are first-time buyers who can afford only modest homes (which qualify for Federal Housing Administration mortgages, the chief form of housing finance during economic downturns). Meanwhile, larger houses are not being built because move-up home buyers are unable to sell their homes in today’s weak housing market.

New York, Los Angeles, San Francisco, and Boston grew modestly during the last two decades. (The size of Chicago and Washington hardly changed.) While these cities did better than the rustbelt cities, whose populations continue to shrink, younger cities such as Colorado Springs, Fort Worth, Atlanta, and Charlotte almost doubled in population during the same period, and Phoenix, San Antonio, and Albuquerque grew by more than a third. What is striking about these new growing cities is that they are much less rather than more dense. New York (the city, not the metropolitan region) contains 26,000 inhabitants per square mile, San Francisco 16,000, Chicago and Boston 12,000, and Washington and Los Angeles slightly fewer, but the new cities of the South and West rarely surpass 3,000 inhabitants per square mile, and the fast-growing city of Charlotte, North Carolina, has fewer than that. Jane Jacobs’s teaching notwithstanding, we appear to be spreading out.

The latest U.S. Census figures reveal that during the last decade, suburban areas outstripped cities in population gains. Moreover, 

reports that “more than a third of all 13.3 million new suburbanites were Hispanic, compared with 2.5 million blacks and 2 million Asians.” At the same time, the immigrant populations of small towns and suburbs increased the most, while those of the big cities remained flat, reversing the historical pattern of the past. Jobs and cheaper housing are strong magnets.

Changes in migration trends are a reminder that Americans have always shown a capacity to adapt. For example, when energy prices spiked in the summer of 2008, people quickly tightened their belts, driving less, walking more, turning down their air conditioners, and shutting off the lights. It is certainly possible that the cold recessionary shower will dampen earlier exuberance and accelerate a shift to urban living, at least among young college graduates and higher-income retirees. The question is whether the rest of us will embrace denser and more compact suburbs and cities, or whether we will depend on technological fixes such as electric and hybrid cars, more efficient heating and cooling systems, and alternative energy sources. I suspect the answer will be a bit of both. Some people will embrace urban density, but many will make sacrifices in order to continue the decentralized way of life they prefer. The heterogeneity that has always characterized American cities will continue to produce many different solutions to suit a large and diverse nation.

 is the Martin and Margy Meyerson Professor of Urbanism at the University of Pennsylvania. He is the author of many books, including, most recently, 

Makeshift Metropolis: Ideas About Cities 

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Americans like their cities spacious. Will concerns about costs and the environment push them to rein in sprawl? 

Dense, Denser, Densest

The models for how we build cities and suburbs have changed significantly in the last two decades.

 Crudely put, the Age of Planning has been replaced by the Age of the Market. This shift is largely the result of the calamitous experience of urban renewal during the 1950s and ’60s, when large swaths of inner city neighborhoods were cleared and replaced by standardized apartment blocks, mammoth public housing projects, and blighting urban expressways. Many cities have still not fully recovered from what amounted to urban lobotomies. This experience gave centralized top-down city planning a bad name, but urbanization itself did not stop—after all, people have to live, shop, and play somewhere.

For the majority of Americans, that “somewhere” has turned out to be the suburbs. The model for the mass-produced suburb emerged fully-formed during the postwar period. The sprawling, standardized communities were focused on the single-family house, assumed car-dependence, and resulted in physical and social fragmentation. In 1993, a meeting in Alexandria, Virginia, brought together architects from around the country who had coalesced around a new suburban model. In the words of Andrés Duany and Elizabeth Plater-Zyberk, two of the founders of the movement that became known as new urbanism, “In order to promote community, the built environment must be diverse in use and population, scaled for the pedestrian, and capable of supporting mass transit as well as the automobile.” 

(Ed. - See their essay “The Second Coming of the American Small Town” in the Winter 1992 

 New urbanism attracted the public because of its traditional architecture and “small town” image; developers liked it because it was a way of developing land at higher densities.

A decade earlier, Seaside, a resort village in Florida, Kentlands in Maryland, and Laguna West, a suburban planned community in California, had demonstrated what such development might be like. They were followed by Celebration outside Orlando, Florida, probably the best executed—certainly the best-known—new urbanist community. It was the result of a collaboration between a far-sighted (and wealthy) client—the Disney Company—and two talented architects, Robert A. M. Stern and Jaquelin T. Robertson. Now more than 15 years old, with 7,500 inhabitants, Celebration demonstrates how various types of housing—large single-family homes as well as townhouses and apartments—can be combined to create many of the qualities of a traditional town. Celebration stresses walkability and density, although it still depends heavily on private automobiles. Like other new urbanist communities, Celebration’s layout is a throwback to the garden suburbs of the early 20th century, but adapted to late-20th-century lifestyles.

That this new model emerged during the housing market boom of the 1980s was no accident. Not only was demand strong enough so that any project had a chance of success, the boom opened the door to inexperienced developers and lenders who were willing to try new ideas. It was only after these neophytes had enjoyed some measure of success that large firms such as Disney embraced the concept. While the first projects tended to be built on outlying virgin sites, which were unencumbered by regulations and surrounding neighbors, later new urbanist projects have moved to urban infill sites. These initiatives have been of varying sizes: Stapleton in Denver, on the site of the old airport, and benefitting from mass transit and proximity to downtown, will eventually have 30,000 inhabitants; Atlantic Station, a 138-acre project in Atlanta, is likewise in a central location; University Place is a small residential neighborhood close to downtown Memphis.

University Place is a so-called Hope VI project. Hope VI is a federal program, begun in 1992, that replaces 1950s-era public housing projects with mixed social and market housing planned according to new urbanist principles. To date, 170,000 units of Hope VI housing have been built. The program is not without its critics, who point out that the largely low- and mid-rise Hope VI housing is not a one-for-one replacement of the high-rise public housing, while proponents argue that in most cases the dysfunctional public housing towers were largely empty. It should also be said that the mixing of public housing, workforce housing (which is partially subsidized), and units sold and rented at market rates, is a social experiment whose success it is still to early to judge.

One of the attractions of places like Celebration and Stapleton is nearby, walkable, shopping streets, a signal of a change in Americans’ shopping habits. Since the 1960s, large indoor shopping malls have been the model for shopping, even in cities. But while the malls in the best locations have continued to prosper, nobody builds new malls anymore and many older malls are being shuttered. This downturn is due to overbuilding, a decline in the fortunes of many department stores (which were the traditional anchors for shopping malls), changes in shopping patterns that favor convenience over a more leisurely experience, competition from big-box stores and discount retailers—especially Walmart—and to a lesser extent, the gradual shift to online shopping.

The two shopping formats that have replaced the mall are at opposite ends of a spectrum. At the no-frills end is the power center, consisting of several big box discount stores such as Best Buy and Petco surrounding a parking lot. Largely a response to shoppers’ demands for low prices and convenience, power centers are less expensive to build and manage than indoor malls. On the other hand, from a social point of view they are a step backward, since they pare down the traditional shopping experience to its bare bones: get in, shop, get out.

At the other end of the spectrum is the so-called Main Street mall: an outdoor arrangement that dispenses with the indoor concourses of traditional malls and replaces them with a traditional street, cars and all. Some Main Street malls go further and add apartments and offices on the upper floors above the stores and restaurants. In appearance, such a mall resembles a small town main street, with sidewalks, sidewalk cafés, and on-street parking (although it is designed, built and managed by a single owner). Reston Town Center, in Reston, Virginia, resembles the downtown of a small city, with high-rise condominiums, office buildings, and a hotel, as well as sidewalk-oriented shops and restaurants. Not surprisingly, the open-air street model has proved more successful in urban locations than the introverted shopping mall, and open-air Main Street malls have been built in Bethesda, Maryland, West Palm Beach, and Dallas.

Main Street malls are an example of what developers call mixed-use

, a new approach to planning that is a reaction to the earlier practice of physically separating different uses such as residential, shopping, and entertainment. The idea is that mixing uses generates more traffic at different times of the day, and that the uses complement one another. Mixed-use does not mean indiscriminately combining different functions, however. Singles or student housing can be exist in late-night entertainment districts, but family or senior housing require quieter surroundings. Nor is a mixed-use project merely a deconstructed mall; shoppers expect to see local retailers, not just familiar national chains. And design quality, which has traditionally been less important in shopping mall planning, is a crucial factor. One of the pleasures of traditional shopping streets is the variety of the architecture, as well as the detailed design of the public spaces—benches, landscaping, lighting—and successful mixed-use developments provide this experience. The town center of Celebration is a good example of well-designed mixed use. Arcaded shops of different sizes line the sidewalks, with apartments on upper levels; parking is discreetly fitted into the center of the block. Low-rise office buildings are located next to condominiums; one street corner is occupied by a small hotel.

The new reality of the last few decades is that developers have replaced city planners as the chief actors in urban development. This has happened not only because city planning lost credibility after the urban renewal debacle, but also because the real estate industry changed. Most developers in the past worked in small, family-owned firms, but increasingly these have been overshadowed by large professionally managed corporations, many of which are publicly-owned companies that operate on a national scale. One of the lessons of the urban renewal period was that thanks to short election cycles, large urban projects that took decades to complete were difficult for city administrations to implement successfully. Paradoxically, large well-funded companies such as Forest City, the developer of Stapleton and Atlantic Yards in Brooklyn, are in a better position to take the long view.

Developers are also better than public agencies at figuring out what people want—and how best to deliver it. Waterfront developments, for example, have proved remarkably popular, as have Main Street malls. But the shift from public to private planning is not an unalloyed good. The concerns of developers naturally tend to be parochial and restricted to their own projects, which are designed and marketed as branded, stand-alone entities. As a result, new development is often not well integrated with the surrounding city. Nor does the developer have the incentive or, indeed, the tools, to deal with larger issues such as urban infrastructure.

One solution is private-public collaboration, and indeed the projects that have been most successfully integrated with their surroundings have tended to be private-public partnerships, with the public body providing those functions that private developers find difficult or impossible to undertake. Two good examples are both urban infill projects underway in Washington, D.C. The Yards occupies 42 acres in the southeast section of the city, on the site of a decommissioned Navy shipyard. Since this is federal land, the General Services Administration is involved in the planning. The result includes a public park, preserved historic buildings, and a plan that is well integrated with the Anacostia River waterfront and the Washington street grid. CityCenter occupies a 10-acre superblock downtown, previously the site of a convention center. With the collaboration of the city government, the project reintroduces previously closed streets and lanes into the superblock site. Once completed, the new buildings will form a seamless whole with their surroundings.

The challenges of the next two decades include not only infilling empty urban sites. A more daunting issue is housing density. Assuming that energy prices continue to rise over time and that some sort of government regulation of carbon emissions will come into effect, energy conservation will become a paramount concern. Mass transit and walkable communities are two logical responses, but they can only function successfully with relatively high urban densities—higher than most American downtowns. Yet the thriving and dense downtowns of New York, Philadelphia, Chicago, Boston, and San Francisco suggest that a significant portion of the millennial generation is attracted to just such urban environments. Downtowns have successfully attracted two groups in recent years—childless young professionals and retirees; the challenge is to make urban living appealing to families. Obviously, better public schools are part of any solution, indeed, without themit is unlikely that downtown populations will become more diverse.

What are the solutions to denser downtown living? One is sometimes called “the Vancouver model”—extremely slim residential high-rise towers sitting on bases consisting of townhouses that create a traditional streetscape. Downtown Vancouver has adopted high-rise living at a density that rivals Asian cities such as Singapore and Hong Kong. But Vancouver is the only North American city to do so. A less drastic solution is medium-rise/high-density housing, such as townhouses and walk-up apartments. While the urban housing built during the 2000-2008 period was aimed at buyers with relatively high incomes, one challenge of the future will be to develop housing that is more family-friendly and definitely cheaper.

There are many different models for dense urban living, but few examples of how to densify suburbs.

 Once the housing industry revives—whenever that happens—the demand for far-out, exurban locations is unlikely to rebound. Higher gasoline prices, and a generally more conservative approach to risk on the part of developers in the wake of the recent housing collapse, will see to that. But it is unlikely that Americans’ preference for single-family houses and suburban lifestyles will drastically change. Where will tomorrow’s new houses be built?

They could occupy infill or replacement parcels in suburban communities on the periphery of central city districts. The overbuilding of retail space in the last several decades means that the sites of shuttered malls will also be prime candidates for redevelopment. But at some point the delicate issue of increasing the population density of existing suburbs will have to be broached. Suburban densification requires that communities revise existing zoning regulations in order to allow the subdivision of lots, taller buildings, multifamily housing, and an increase in mixed-use development. Creating walkable town centers requires rethinking zoning that previously prevented commercial enterprises in housing areas. The corner store was once a staple of the American neighborhoods—it could return. Walkable streets and corner stores—it’s hardly rocket science. What we need is not particularly difficult or complicated, but given the historical resistance to change and especially to any measure that even slightly increases housing density and traffic, how to get it done will be the real challenge.

 is emeritus professor of urbanism at the University of Pennsylvania. His first article in 

 appeared in the Summer 1992 issue. His latest book is 

The Biography of a Building: How Robert Sainsbury and Norman Foster Built a Great Museum

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A better approach to shaping the places in which we live has emerged just as Americans responding to the rising cost of energy begin to crowd into older suburbs and cities.

Witold Rybczynski