This paper suggests a cause of low density urban development or urban sprawl that has not been given much attention in the literature. There have been a number of arguments put forward for market failures that may account for urban sprawl, including incomplete pricing of infrastructure, environmental externalities, and unpriced congestion. The problem analyzed here is that urban growth creates benefits for an entire urban area, but the costs of growth are borne by individual neighbourhoods. An externality problem arises because existing residents perceive the costs associated with the new residents locating in their neighbourhoods, but not the full benefits of new entrants which accrue to the city as a whole. The result is that existing residents have an incentive to block new residents to their neighbourhoods, resulting in cities that are less dense than is optimal, or too spread out. The paper models several different types of urban growth, and examines the optimal and local choice outcomes under each type. In the first model, population growth is endogenous and the physical limits of the city are fixed. The second model examines the case in which population growth in the region is given, but the city boundary is allowed to vary. We show that in both cases the city will tend to be larger and less dense than is optimal. In each, we examine the sensitivity of the model to the number of neighbourhoods and to the size of infrastructure and transportation costs. Finally, we examine optimal subsidies and see how they compare to current policies such as impact fees on new development.
Urban sprawl or suburban sprawl is a multifaceted concept centered on the expansion of auto-oriented, low-density development. Topics range from the outward spreading of a city and its suburbs, to low-density and auto-dependent development on rural land, examination of impact of high segregation between residential and commercial uses, and analysis of various design features to determine which may encourage car dependency. The term "sprawl" is most often associated with US land use; outside the US (and especially outside the Anglosphere), the term "peri-urbanisation" is often used to denote similar dynamics and phenomena.
Sprawl are often made unclear by the uncertainty of the meaning 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 centre), discontinuity (leapfrog development, as defined below), segregation of uses, and so forth.
The term urban sprawl generally has negative connotations due to the health, environmental and cultural issues associated with the phrase. Residents of sprawling neighbourhoods tend to emit more pollution per person and suffer more traffic fatalities. Sprawl is controversial, with supporters claiming that consumers prefer lower density neighbourhoods and that sprawl does not necessarily increase traffic. Others have argued that sprawl is less a reflection of consumer preferences and more a result of legal structures and court decisions that have encouraged sprawl development.
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 fewer 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 is growing.
Overall density is often lowered by "leapfrog 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. 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.
CAUSES OF URBAN SPRAWLS
Urban sprawl is loosely defined as low-density residential, and sometimes commercial, development that is outside the borders of higher density urban centers. Urban sprawl communities are typically automobile-oriented as opposed to pedestrian-friendly. Planners, scholars, community activists and public officials all offer numerous possibilities as to the causes of urban sprawl.
Lack of Comprehensive Planning
The Planners Web Sprawl Guide suggests that little to no regional planning is one of the major causes of urban sprawl. If officials in densely populated urban centers plan in isolation without consulting nearby communities, the result is sometimes poorly planned developments on the outskirts of urban centers. Instead of bridging the existing infrastructure and amenities of surrounding communities, these less densely populated areas often incur new public expenses for infrastructure improvements without regard to a regional plan or pooled resources. A regional plan would anticipate the growth of new areas and gradually execute the necessary planning initiatives to create a cohesive community.
Rapid Population Growth
The Sierra Club notes that although population growth is not the only cause of urban sprawl, it is a major factor. Rapid population growth is a particularly large contributor to urban sprawl in the Western and Southern regions of the United States. A sharp increase in residents beyond the capacity of nearby urban centers necessitates the creation of new communities. As the regional population continues to increase, communities begin to spread farther and farther away from city centers.
Subsidized Infrastructure Improvements
One condition that encourages urban sprawl, according to Towson University Center for Geographic Information Sciences, occurs when municipalities subsidize the cost of infrastructure such as roads and sewers to un- or under-developed areas. Such an action incentivizes the creation of communities outside of city centers without requiring comprehensive plans or suggesting alternative development options.
One cause of urban sprawl that is difficult to quantify is preference. Useful Community Development, a site dedicated to progressive urban planning, cites the desire for larger homes, more bedrooms and bigger yards as one of the causes of urban sprawl. Some people simply prefer more space or more home square footage than what is affordable or available in more crowded city centers.
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