Urban sprawl, also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its suburbs to its outskirts to low-density, auto-dependent development on rural land, with associated design features that encourage car dependency. As a result, some critics argue that sprawl has certain disadvantages, including:
Discussions and debates about sprawl are often obfuscated by the ambiguity associated with the phrase. For example, some commentators measure sprawl only with the average number of residential units per acre in a given area. But others associate it with decentralization (spread of population without a well-defined center), discontinuity (leapfrog development, as defined below), segregation of uses, etc. (See Wrestling Sprawl to the Ground; Defining and Measuring an Elusive Concept for a detailed analysis of these definitions).
The term urban sprawl generally has negative connotations due to the health, environmental and cultural issues associated with the phrase. Residents of sprawling neighborhoods tend to emit more pollution per person and suffer more traffic fatalities. Sprawl is controversial, with supporters claiming that consumers prefer lower density neighborhoods and that sprawl does not necessarily increase traffic. Sprawl is also linked with increased obesity since walking and bicycling are not viable commuting options. Sprawl negatively impacts land, air, and water quality, and may be linked to a decline in social capital.
Sprawl is characterized by several land use patterns which usually occur in unison:
This refers to a situation where commercial, residential, institutional and industrial areas are separated from one another. Consequently, large tracts of land are devoted to a single use and are segregated from one another by open space, infrastructure, or other barriers. As a result, the places where people live, work, shop, and recreate are far from one another, usually to the extent that walking, transit use and bicycling are impractical, so all these activities generally require an automobile.
Sprawl consumes much more land per-capita than traditional urban developments because zoning laws generally require that new developments are of low density. The exact definition of "low density" is arguable, but a common example is that of single family homes on large lots, with four or less units per net acre. Buildings usually have fewer stories and are spaced farther apart, separated by lawns, landscaping, roads or parking lots. Lot sizes are larger, and because more automobiles are used much more land is designated for parking. The impact of low density development in many communities is that developed or "urbanized" land is increasing at a faster rate than the population.
Overall density is often lowered by "leap-frog development". This term refers to the relationship, or lack thereof, between subdivisions. Such developments are typically separated by large green belts, i.e. tracts of undeveloped land, resulting in an average density far lower even than the low density described in the previous paragraph. This is a 20th and 21st century phenomenon generated by the current custom of requiring a developer to provide subdivision infrastructure as a condition of development (DeGrove and Turner, 1991). Usually, the developer is required to set aside a certain percentage of the developed land for public use, including roads, parks and schools. In the past, when a local government built all the streets in a given location, the town could expand without interruption and with a coherent circulation system, because it had condemnation power. Private developers generally do not have such power (although they can sometimes find local governments willing to help), and often choose to develop on the tracts that happen to be for sale at the time they want to build, rather than pay extra or wait for a more appropriate location.
Areas of urban sprawl are also characterized as highly dependent on automobiles for transportation, a condition known as automobile dependency. Most activities, such as shopping and commuting to work, require the use of a car as a result of both the area's isolation from the city and the isolation the area's residential zones have from its industrial and commercial zones. Walking and other methods of transit are not practical; therefore, many of these areas have few or no sidewalks. In many suburban communities, stores and activities that are in close proximity "as the crow flies" require automobiles, because the different areas are separated by fences, walls, and drainage ditches. Some critics argue that excessive parking requirements exaserbate car dependency.
Job Sprawl is another land use symptom of urban sprawl and car-dependent communities. It is defined as low-density, geographically spread-out patterns of employment, where the majority of jobs in a given metropolitan area are located outside of the main city's Central Business District (CBD), and increasingly in the suburban periphery. It is often the result of urban disinvestment, the geographic freedom of employment location allowed by predominantly car-dependent commuting patterns of many American suburbs, and many companies' desire to locate in low-density areas that are often more affordable and offer potential for expansion. Spatial mismatch is related to job sprawl and economic Environmental Justice. Spatial Mismatch is defined as the situation where poor urban, predominantly minority citizens are left without easy access to entry-level jobs, as a result of increasing job sprawl and limited transportation options to facilitate a reverse commute to the suburbs.
Job sprawl has been documented and measured in various ways. It has been shown to be a growing trend in America's metropolitan areas. The Brookings Institution has published multiple articles on the topic. In 2005, author Michael Stoll defined job sprawl simply as jobs located more than 5-mile radius from the CBD, and measured the concept based on year 2000 U.S. Census data.  Other ways of measuring the concept with more detailed rings around the CBD include a 2001 article by Edward Glaeser  and Elizabeth Kneebone's 2009 article, which show that sprawling urban peripheries are gaining employment while areas closer to the CBD are losing jobs.  These two authors used three geographic rings limited to a 35-mile radius around the CBD: 3 miles or less, 3 to 10 miles, and 10 to 35 miles. Kneebone's study showed the following nationwide breakdown for the largest metropolitan areas in 2006: 21.3% of jobs located in the inner ring, 33.6% of jobs in the 3-10 mile ring, and 45.1% in the 10-35 mile ring. This compares to the year 1998 - 23.3%, 34.2%, and 42.5% in those respective rings. The study shows CBD employment share shrinking, and job growth focused in the suburban and exurban outer metropolitan rings.
In terms of measurement, spatial mismatch can be thought of as the percentage of people who would have to move in order to be distributed in the same way as jobs. Stoll's research shows that a substantially higher percentage of African Americans (53.5%) experience spatial mismatch than white citizens (35.6%). On average, more than half of African American citizens would need to move to accomplish similar distribution to jobs. Latinos (45.8%) experience spatial mismatch as well, though to a lesser extent than African Americans.
Housing subdivisions are large tracts of land consisting entirely of newly-built residences. Prominent new urbanist architects Duany and Plater-Zyberk claim that housing subdivisions “are sometimes called villages, towns, and neighborhoods by their developers, which is misleading since those terms denote places which are not exclusively residential.” They are also referred to as developments.
Subdivisions often incorporate curved roads and cul-de-sacs. Such subdivisions may offer only a few places to enter and exit the development, causing traffic to use high volume collector streets. All trips, no matter how short, must enter the collector road in a suburban system. (Duany Plater-Zyberk 5, 34)
Shopping centers are locations consisting of retail space. In the U.S. and Canada, these vary from strip malls which refer to collections of buildings sharing a common parking lot, usually built on a high-capacity roadway with commercial functions (i.e., a "strip"). Similar developments in the UK are called Retail Parks. Strip malls/retail parks contain a wide variety of retail and non-retail functions that also cater to daily use (e.g. video rental, takeout food, laundry services, hairdresser). Strip malls consisting mostly of big box stores or category killers are sometimes called "power centers" (U.S.). These developments tend to be low-density; the buildings are single-story and there is ample space for parking and access for delivery vehicles. This character is reflected in the spacious landscaping of the parking lots and walkways and clear signage of the retail establishments. Some strip malls are undergoing a transformation into Lifestyle centers; entailing investments in common areas and facilities (plazas, cafes) and shifting tenancy from daily goods to recreational shopping. European countries such as France, Belgium and Germany have implemented size restrictions for superstores found in strip malls in an effort to limit sprawl (Davies 1995).
Another prominent form of retail development in areas characterized by "sprawl" is the shopping mall. Unlike the strip mall, this is usually composed of a single building surrounded by a parking lot which contains multiple shops, usually "anchored" by one or more department stores (Gruen and Smith 1960). The function and size is also distinct from the strip mall. The focus is almost exclusively on recreational shopping rather than daily goods. Shopping malls also tend to serve a wider (regional) public and require higher-order infrastructure such as highway access and can have floorspaces in excess of a million square feet (ca. 100,000 m²). Shopping malls are often detrimental to downtown shopping centers of nearby cities since the shopping malls acts as a surrogate for the city center (Crawford 1992). Some downtowns have responded to this challenge by building shopping centers of their own (Frieden and Sagelyn 1989; consider also Toronto Eaton Centre (1977), Ottawa's Rideau Centre, Boston's Shops at Prudential Center, and Providence's Providence Place).
In the 1970s, the Ontario government created the Ontario Downtown Renewal Programme, which helped finance the building of several downtown malls across Ontario (such as the aforementioned Eaton Centre). The program was created to reverse the tide of small business leaving downtowns for larger sites surrounding the city.
Fast food chains are common in suburban areas. They are often built early in areas with low property values where the population is expected to boom and where large traffic is predicted, and set a precedent for future development. Eric Schlosser, in his book Fast Food Nation, argues that fast food chains accelerate suburban sprawl and help set its tone with their expansive parking lots, flashy signs, and plastic architecture (65). Duany Plater Zyberk & Company believe that this reinforces a destructive pattern of growth in an endless quest to move away from the sprawl that only results in creating more of it (Duany Plater-Zyberk 26).
According to the National Resources Inventory (NRI), about 8,900 square kilometers (2.2 million acres) of land in the United States was developed between 1992 and 2002. Presently, the NRI classifies approximately 100,000 more square kilometers (40,000 square miles) (an area approximately the size of Kentucky) as developed than the Census Bureau classifies as urban. The difference in the NRI classification is that it includes rural development, which by definition cannot be considered to be "urban" sprawl. Currently, according to the 2000 Census, approximately 2.6 percent of the U.S. land area is urban. Approximately 0.8 percent of the nation's land is in the 37 urbanized areas with more than 1,000,000 population. In 2002, these 37 urbanized areas supported around 40% of the total American population.
Nonetheless, some urban areas have expanded geographically even while losing population. But it was not just urbanized areas in the U.S. that lost population and sprawled substantially. According to data in "Cities and Automobile Dependence" by Kenworthy and Laube (1999), urbanized area population losses occurred while there was an expansion of sprawl between 1970 and 1990 in Brussels, Belgium; Copenhagen, Denmark; Frankfurt, Hamburg, and Munich, Germany; and Zurich, Switzerland, albeit without the wholesale dismantling of public transit systems that occurred in the United States.
At the same time, the urban cores of these and nearly all other major cities in the United States, Western Europe, and Japan that did not annex new territory experienced the related phenomena of falling household size and, particularly in the U.S., "white flight", sustaining population losses. This trend has slowed somewhat in recent years, as more people have regained an interest in urban living.
The term Los Angelization is also sometimes used for urban sprawl, though this may be misleading. Los Angeles was one of the world's first low density urbanized areas, as a result of wide automobile ownership. However, Los Angeles has become more dense over the past half-century, principally due to small lot zoning and a high demand for housing due to population growth. Los Angeles increased its density to 2240/km² (5,801 per square mile) in 1990. Land consumption per resident in 1990 was 0.11-acre (450 m2), which made Los Angeles the most densely populated urbanized area in the United States. It should be pointed out, however, that average density is not the only measure of sprawl; some urbanists argue that the city's car-dependent, decentralized form is itself a type of "sprawl" development.
Urban sprawl is not limited to developed countries, and may be more prevalent in developing countries. For example, there is considerable land consumed by urban sprawl in Mexico City, in Beijing, in Antananarivo (the capital of Madagascar), in Johannesburg, and in eastern parts of South Africa.
The first urban growth boundary in the U.S. was in Fayette County, Kentucky in 1958. Fifteen years later, the state of Oregon enacted a law in 1973 limiting the area urban areas could occupy, through urban growth boundaries. As a result, Portland, the state's largest urban area, has become a leader in smart growth policies that seek to make urban areas more compact (they are called urban consolidation policies). After the creation of this boundary, the population density of the urbanized area increased somewhat (from 1,135 in 1970 to 1,290 per km² in 2000) USA Urbanized Areas 1950-1990 USA Urbanized Areas 2000. While the growth boundary has not been tight enough to vastly increase density, the consensus is that the growth boundaries have protected great amounts of wild areas and farmland around the metro area.
Many parts of the San Francisco Bay Area have also adopted urban growth boundaries; 25 of its cities and 5 of its counties have urban growth boundaries. Many of these were adopted with the support and advocacy of Greenbelt Alliance, a non-profit land conservation and urban planning organization.
While cities such as Chicago are well known for sprawling suburbs, policies and public opinion are changing. Transit-oriented development, in which higher-density mixed-use areas are permitted or encouraged near transit stops is encouraging more compact development in certain areas-particularly those with light and heavy heavy rail transit systems.
Arguments opposing urban sprawl run the gamut from the more concrete effects such as health and environmental issues to more abstract consequences involving neighborhood vitality.
Urban sprawl is associated with a number of negative environmental and public health outcomes, with the primary result being increased dependence on automobiles.
However, this is mitigated significantly with nearby development of shopping and recreation areas. Also, many people prefer to live close to their place of business which is increasingly centered less around urban areas.
In the years following World War II, when vehicle ownership was becoming widespread, public health officials recommended the health benefits of suburbs due to soot and industrial fumes in the city center. However, air in modern suburbs is not necessarily cleaner than air in urban neighborhoods. In fact, the most polluted air is on crowded highways, where people in suburbs tend to spend more time. On average, suburban residents generate more per capita pollution and carbon emissions than their urban counterparts because of their increased driving.
A heavy reliance on automobiles increases traffic throughout the city as well as automobile crashes, pedestrian injuries, and air pollution. Motor vehicle crashes are the leading cause of death for Americans between the ages of five and twenty-four and is the leading accident-related cause for all age groups. Residents of more sprawling areas are at greater risk of dying in a car crash.
The American Journal of Public Health and the American Journal of Health Promotion, have both stated that there is a significant connection between sprawl, obesity, and hypertension. Many urbanists argue that this is due to less walking in sprawl-type developments. Living in a car centered culture forces inhabitants to drive everywhere, thus walking far less than their urban (and generally healthier) counterparts.
Urban sprawl may be partly responsible for the decline in social capital in the United States. Compact neighborhoods can foster casual social interactions among neighbors, while sprawl creates barriers. Sprawl tends to replace public spaces with private spaces such as fenced-in backyards.
Due to the larger area consumed by sprawling suburbs compared to urban neighborhoods, more farmland and wildlife habitats are displaced per resident. As forest cover is cleared and covered with impervious surfaces (concrete and asphalt) in the suburbs, rainfall is less effectively absorbed into the ground water aquifers. This threatens both the quality and quantity of water supplies. Sprawl increases water pollution as rain water picks up gasoline, motor oil, heavy metals, and other pollutants in runoff from parking lots and roads. Sprawl fragments the land which increases the risk of invasive species spreading into the remaining forest.
Living in larger, more spread out spaces generally makes public services more expensive. Since car usage becomes endemic and public transport often becomes significantly more expensive, city planners are forced to build large highway and parking infrastructure, which in turn decreases taxable land and revenue, and decreases the desirability of the area adjacent to such structures. Providing services such as water, sewers, and electricity is also more expensive per household in less dense areas.
Residents of low-density areas spend a higher proportion of their income on transportation than residents of high density areas. The RAC estimates that the average cost of operating a car in the UK is £5,000 a year. In comparison, a yearly underground ticket for a suburban commuter in London (where wages are higher than the national average) costs £1,000-1,500.
Critics of sprawl maintain that quality of life is eroded by lifestyles promoted by sprawl promotes. Duany and Plater-Zyberk believe that in traditional neighborhoods the nearness of the workplace to retail and restaurant space that provides cafes and convenience stores with daytime customers is an essential component to the successful balance of urban life. Furthermore, they state that the closeness of the workplace to homes also gives people the option of walking or riding a bicycle to work or school and that without this kind of interaction between the different components of life the urban pattern quickly falls apart. (Duany Plater-Zyberk 6, 28). James Howard Kunstler has argued that poor aesthetics in suburban environments make them "places not worth caring about", and that they lack a sense of history and identity.
Some blame suburbs for what they see as a homogeneity of society and culture, leading to sprawling suburban developments of people with similar race, background and socioeconomic status. They claim that segregated and stratified development was institutionalized in the early 1950s and 1960s with the financial industries' then-legal process of redlining neighborhoods to prevent certain people from entering and residing in affluent districts. Sprawl may have a negative impact on public schools as finances have been pulled out of city cores and diverted to wealthier suburbs. They argue that the residential and social segregation of whites from blacks in the United States creates a socialization process that limits whites' chances for developing meaningful relationships with blacks and other minorities, and that the segregation experienced by whites from blacks fosters segregated lifestyles and can lead to positive views about themselves and negative views about blacks.
The American Institute of Architects and the American Planning Association recommend against sprawl and instead endorses smart, mixed-use development, including buildings in close proximity to one another that cut down on automobile use, save energy, and promote walkable, healthy, well-designed neighborhoods. The Sierra Club, the San Francisco Bay Area's Greenbelt Alliance, and other environmental organizations oppose sprawl and support investment in existing communities. NumbersUSA, a national organization advocating immigration reduction, also opposes urban sprawl, and its executive director, Roy Beck, specializes in the study of this issue.
Peter Gordon, a professor of planning and economics at the University of Southern California's School of Urban Planning and Development, argues that many households in the United States, Canada, and Australia, especially middle and upper class families, have shown a preference for the suburban lifestyle. Reasons cited include a preference towards lower-density development (for lower ambient noise and increased privacy), better schools, less crime, and a generally slower lifestyle than the urban one. Those in favor of the current pro low-density land use policies also argue that this sort of living situation is an issue of personal choice and economic means. One suburban Detroit politician defends low-density development as the preferred lifestyle choice of his constituents, calling it "...the American Dream unfolding before your eyes."
Those not opposed to low density development argue that traffic intensities tend to be less, traffic speeds faster and, as a result, ambient air pollution is lower. (See demographia's report.) Kansas City, Missouri is often cited as an example of ideal low-density development, with congestion below the mean and home prices below comparable Midwestern cities. Wendell Cox and Randal O'Toole are the leading figures supporting lower density development.
Longitudinal (time-lapse) studies of commute times in major metropolitan areas in the United States have shown that commute times decreased for the period 1969 to 1995 even though the geographic size of the city increased.
There is also some concern that Portland-style anti-sprawl policies will increase housing prices. Some research suggests Oregon has had the largest housing affordability loss in the nation, but other research shows that Portland's price increases are comparable to other Western cities. Another report suggests that zoning and other land use controls play the dominant role in making housing expensive-although it should be pointed out that the majority of zoning and land use polices mandate, rather than forbid, sprawl.
In Australia, it is claimed by some that housing affordability has hit "crisis levels" due to "urban consolidation" policies implemented by state governments. In Sydney, the ratio of the price of a house relative to income is 9:1. The issue was being debated between the major political parties in the lead up to the Australian federal election.
There are some sociologists such as Durkheim who suggest there is a link between population density and the number of rules that must be imposed. The theory goes that as people are moved closer together geographically their actions are more likely to noticeably impact others around them. This potential impact requires the creation of additional social or legal rules to prevent conflict. A simple example would be as houses become closer together the acceptable maximum volume of music decreases, as it becomes intrusive to other residents.
Numerous studies link increased population density with increased aggression. Some people believe that increased population density encourages crime and anti-social behavior. It is argued that human beings, while social animals, need significant amounts of social space or they become agitated and aggressive.