The United States after the turn of the century remains a nation with an expanding population and spreading cities. The suburbanization of America is a long-standing trend, made possible largely by the automobile and encouraged by rising incomes and public policies, including public investment in an extensive highway network. For all the mobility it has provided, automobile transportation has also helped make the nation dependent upon petroleum, with associated adverse health effects of vehicular emissions, dependence on imports, and increasing greenhouse gas (GHG) emissions.
The scale of automotive travel and energy consumption is enormous. Transportation on U.S. roads and highways totaled about 3 trillion vehicle miles traveled (VMT) in 2007 and consumed about 176,100 million gallons of gasoline, virtually all from petroleum (FHWA 2009, Table VM-1). (The transportation sector alone consumes more petroleum than is produced domestically.) Cars and light trucks (most of which are used for personal transportation) account for about 17 percent of total annual U.S. energy consumption (Davis et al. 2008, Table 2.1), and this share has been growing. In addition, gasoline consumption, largely by personal vehicles, accounts for about 20 percent of carbon dioxide (CO2) emissions—the largest source of U.S. GHG emissions, which contribute to global warming (Davis et al. 2008, Tables 11.4 and 11.5).1
The United States has been increasingly reliant on imported petroleum for decades, so why has the energy consumption associated with low-density development patterns become such a prominent concern, motivating this study? Despite the energy shocks of the 1970s and 1980s and many plans to reduce reliance on imported fuels, demand has only grown, stimulated by declining gasoline prices and consumer preferences for larger, less energy-efficient vehicles during the 1990s. But the terrorist attacks of September 11, 2001, followed by instability in various parts of the Middle East and other oil-producing countries (e.g., Venezuela, Nigeria) and the growth of China and India, began a period of rising oil prices. By July 2008, the price of a barrel of crude oil had reached a historic high in real terms, increasing awareness of U.S. vulnerability to imported fuels.2 In addition, concern about climate change continues to rise both domestically and internationally, and transportation is a major and increasing contributor to that growing problem. The United States currently accounts for about 33 percent of world CO2 emissions from road transport (IEA 2006), although emissions have been growing more rapidly in some developing countries, such as China. An additional factor, although less newsworthy, is the health risks resulting from transportation emissions and the difficulty being experienced by many regions in meeting federal clean air standards. At the same time, changing demographics—an aging population, continued immigration— and the possibility of sustained higher energy prices should lead to more opportunities for the kinds of development patterns that could reduce vehicular travel, thereby saving energy and reducing CO2 emissions.
STUDY CHARGE AND SCOPE
The purpose of this study is to examine the relationship between land development patterns and motor vehicle travel in the United States to support an assessment of the scientific basis for and make appropriate
judgments about the energy conservation benefits of more compact development patterns. More specifically, the study request, contained in Section 1827 of the Energy Policy Act of 2005 (see Appendix A), calls for consideration of four topics:
The correlation, if any, between land development patterns and increases in VMT.
An assessment of whether petroleum use in the transportation sector can be reduced through changes in the design of development patterns.
The potential benefits of
Information and education programs for state and local officials (including planning officials) on the potential for energy savings through planning, design, development, and infrastructure decisions;
Incorporation of location efficiency models in transportation infrastructure planning and investments; and
Transportation policies and strategies to help transportation planners manage the demand for and the number and length of vehicle trips, including trips that increase the viability of other means of travel.
Any other relevant topics deemed appropriate for consideration.
The study committee interpreted its charge by both expanding and consolidating the scope. The most important addition was an assessment of the potential benefits of more compact development in reducing CO2 emissions, which can readily be derived from estimates of reduced petroleum use.3 On the other hand, the committee determined that evaluating the potential benefits of information and education programs was not feasible through a scientific assessment because the
link between such programs and policy outcomes in this arena is too tenuous to be established reliably from the literature. Nevertheless, the committee considered the more general political and institutional context of land development policies both in illustrative case studies and as an important factor in policy implementation. In sum, the committee reorganized its charge into two main components: (a) an assessment of the impact of land development patterns, specifically more compact development, on VMT,4 and (b) an estimate of the potential energy savings and reductions in CO2 emissions resulting from land use policies that reduce VMT.
The study is focused on land development patterns and motor vehicle travel in metropolitan areas of the United States, where more compact development would have the greatest effect. International studies and experience with compact development are considered to the extent that the comparisons are relevant. Decentralized responsibility for land use planning and many other institutional and political differences between the United States and other countries, however, limit the applicability of international experience. The study is also focused primarily on personal travel. Policies that encourage more compact development could affect metropolitan freight distribution and delivery patterns—a topic examined in this study—but those policies target mainly residential and employment location decisions and personal travel.5
The remainder of this chapter provides an overview of trends in VMT growth and the primary determinants of that growth. Then, development strategies for curbing VMT are introduced, and the broader context for their merits and limitations is briefly examined. The chapter ends with a summary of the organization of the report.
TRENDS IN VMT GROWTH
For several decades, passenger vehicle travel on U.S. highways has been increasing at a much faster rate than either population or developed land (see Figure 1-1).6 Low-density development, which has been the dominant U.S. development pattern for generations, spreads destinations farther apart and therefore necessitates longer distances to complete trips. Attributing increased travel to such development patterns has intuitive appeal. However, the factors
VMT statistics are for passenger cars; motorcycles; and other two-axle, four-wheeled vehicles, which include vans, pickup trucks, and sport utility vehicles. The data on developed land are from the National Resources Inventory (NRI), described in Chapter 2; these data are not available before 1982, hence the starting date for the graph. The most recent NRI data on developed land are from 2003. The distortion in the x-axis is due to the irregular years for which developed land data are available.
affecting VMT growth are far more complex. Like passenger vehicle travel, for example, real disposable personal income has risen more rapidly than either population or developed land. The effects of higher income on highway passenger vehicle travel are manifested in higher levels of automobile ownership and growth in the proportion of households owning multiple vehicles; these trends in turn not only increase trips and travel but also reduce the number of trips made by transit or walking and increase the number of discretionary trips (Memmott 2007).7 Another plausible explanation for the high rate of growth of VMT during this period is the higher proportion of the driving-age population that became licensed as women completed their entry into the labor force. By 2001, as a result of the confluence of these various factors, 93 percent of all U.S. households owned at least one vehicle (Memmott 2007, 2).
Since about 1997, however, incomes have apparently been rising somewhat more rapidly than VMT, perhaps because of saturation of automobile ownership and the increasing time cost of travel due to congestion. Recent rising gasoline prices (not shown on Figure 1-1), followed by the current recession, have also reduced the growth of VMT, but it remains to be seen whether the reduction will continue.8
Of interest, growth in highway passenger vehicle VMT does not track especially well with fuel consumption (see Figure 1-1). Between 1982 and 2007, VMT rose by 189 percent, while passenger vehicle fuel consumption increased by 148 percent, leveling out after 2001.9 Presumably, improved fuel economy reduced some of the energy use from VMT growth over this period.
The broad trends shown on Figure 1-1 tend to mask the diversity of development patterns and travel within metropolitan areas, a topic addressed more fully in the next chapter. Developed land, for example, can range from 2-acre lots with single-family homes in suburban areas; to ¼- to ⅛-acre lots with single-family homes in the inner suburbs; to much more densely developed multifamily housing, often near office and retail complexes, at densities high enough to support transit. Each of these different development patterns and their locations in a region help determine the length and frequency of trips and the mode of travel employed.
DEVELOPMENT STRATEGIES TO CURB VMT GROWTH
History and Measurement of Land Development Patterns
Current land development patterns, frequently referred to as the built environment, have evolved over many decades, if not generations.10 The growth of U.S. metropolitan areas and the decentralization of population to lower-density residential areas within central cities and to outlying suburbs can be traced back to at least the 1880s (NRC 1999) and in some cities to the 1810s (Jackson 1985).
During the industrial age, cities grew intensely crowded in the United States and Europe. Most urban dwellers lived in poor housing where they faced high levels of pollution and natural hazards and low levels of public services and open space. The laying of streetcar lines by wealthy U.S. landowners in the latter third of the 19th century enabled the middle class to escape the ills of overcrowded cities, giving rise to the first wave of suburbanization (Warner 1978). Only a small fraction of affluent families, however, could afford to move to the suburbs. In the early 1900s, city planners advocated measures to reduce density
and separate land uses. In tune with their recommendations, state governments began to adopt zoning and subdivision reform in the 1920s, and in the 1930s the New Deal brought federal involvement with mortgage insurance, highway planning, and public housing legislation. These reforms set the stage for mass middle-class suburbanization in the postwar period, which was complemented by massive public transportation infrastructure investment in the Interstate Highway System.11
As early as the mid-1960s, however, many observers began to see that low-density and separated uses, which encouraged automobile dependence, would cause as many problems as they solved. As the environmental movement was born, critics of mass suburbanization began using the phrase urban sprawl to describe the low-density, dispersed, single-use, automobile-dependent built environment that— in their view—wasted energy, land, and other resources and exacerbated racial divisions (Burchell et al. 2002).12
Since the 1960s, at least two waves of planning reform have elevated land development patterns to national prominence. In the 1980s, suburb-to-suburb commuting led to a significant increase in traffic, prompting the creation of new growth management initiatives, some of which sought to contain spreading cities through such measures as urban growth boundaries. In the 1990s, fueled by large-lot development at the urban fringes, the smart growth movement discussed later in this chapter changed the development debate from the traditional emphasis on growth/no growth to a focus on how and where new development could best be accommodated (Knaap 2006).
Until recently, land use reformers had not defined sprawl very precisely; advocates liked the word partly because of its conceptual fuzziness
(Markusen 1999). Better practice and replicable modeling, however, demanded more rigor. Responding to the need for clarity, academic observers began to sharpen measures to distinguish the real effects (and causes) of a variety of land development patterns. Consensus has now emerged on some of the important dimensions on which land development patterns should be measured, although work on quantifying the consequences of these patterns is still in its infancy.
Most observers agree that density is an essential dimension of land development patterns and seek to test whether (as suspected) low-density development has a variety of harmful consequences. Recent literature stresses the importance of measuring density on the basis of people (residents, households, or businesses) or buildings (houses, business spaces) per acre of developed land, as opposed to using overall land area within a city or county as the denominator (see, for example, Fulton et al. 2001; Galster et al. 2001; Carruthers and Úlfarsson 2008).13 A second critical measure is the mix of land uses within neighborhoods and districts; a land use pattern in which highly complementary activities are separated in space is considered more sprawling (Cervero and Kockelman 1997; Galster et al. 2001; Ewing et al. 2002). Third, the concentration of development in one or more high-density centers of employment (or mixed-use centers) outside the central business district is hypothesized to have potentially important effects on travel, facilitating transit use and walking and shortening automobile commute trips by bringing jobs closer to housing. Researchers, however, are in less agreement about either the measurement or the potential impact of centering. Fourth, a range of measurements describe the spatial arrangement or contiguity of land uses with respect to each other.
Key concerns include, for example, the relationship between developed and undeveloped land and the average proximity of business and residential uses. Development that is discontinuous—that leapfrogs beyond undeveloped land—is considered more sprawling (Galster et al. 2001). A fifth area under consideration and measurement is the design of street fronts and neighborhoods in ways that encourage walking and bicycling (e.g., presence of attractive houses and stores, shade, planting) (Cervero and Kockelman 1997).
As measurement of land uses has progressed, so, too, has that of transportation systems and their relationship to land use. Transportation networks complement and interact with land development patterns, necessitating independent measurement of transportation networks and their relationship to development (Ewing and Cervero 2001). One key set of transportation infrastructure measures concerns the spatial pattern of transportation networks: whether they are sparse or dense; whether they are arranged in grids that improve connectivity versus a hierarchy of streets resembling the branching of rivers, trees, or blood vessels that may lead to circuitous routes or end in cul-de-sacs; whether they feature a strong fixed-rail transit network; and so on. Two other characteristics measure how transportation networks interact with development patterns to affect accessibility. Destination accessibility measures the ease or convenience of trip destinations relative to point of origin and is often measured at the regional level in terms of distance relative to the central business district or other major centers (Ewing and Cervero 2001). Distance between development and transit, either rail stations or bus stops, has been thought to have a separate and significant effect on the likelihood that people will use transit.
Various strategies are being tried to counter sprawl, including increasing the density, mix, contiguity, connectedness, and pedestrian orientation of development and implementing steps to encourage nonautomotive
travel. These strategies are referred to by such terms as transit-oriented development, neotraditional design, and smart growth. The smart growth movement, for example, is a broad coalition of interests representing land and historic building trusts, environmental groups, planning organizations, and public interest groups and is often associated with advocacy positions. For purposes of this report, the committee sought a more neutral term; hence, strategies to reduce sprawl are all referred to as more compact, mixed-use development.
The Broader Context
The topics of sprawl and compact, mixed-use development are often contentious.14 Proponents of more compact development see various possible benefits from future land use patterns that concentrate more housing and employment on less acreage. More compact development reduces distances between origins and destinations, thereby reducing trip lengths and VMT.15 To the extent that more compact development encourages transit and nonmotorized travel, it may also reduce congestion and air pollution. Debate on the merits of antisprawl, compact development, however, turns on more than density and reduction of automobile dependence and VMT. More compact development also reduces the cost of providing infrastructure, increases the feasibility and cost-effectiveness of transit, increases the feasibility of providing moderately priced housing and provides more housing choices, and may foster a greater sense of community. Other benefits include less demand for undeveloped land and for conversion of agricultural and other lands, including environmentally fragile areas, such as wetlands and sensitive watersheds (Burchell et al. 2005). Finally, less development of land reduces runoff into streams and receiving waters and preserves open space.
Critics of compact development claim that proponents ignore its costs. Although a good argument can be made that compact, mixed-use development is undersupplied to meet existing demand (Levine 2005), the higher densities of most compact developments involve trade-offs.16 They allow, for example, less personal space for individuals and families than has been the norm for many new residential developments, often entailing more housing units on an acre of land than has been typical in recent decades. Whether this would be perceived as an undesirable cost for many—and in particular the extent to which higher residential density would require a shift from detached single-family to attached housing styles—is explored later in this report. Neither proponents nor critics of compact development are well informed about how people’s housing preferences are formed or how they might change in the future, the topic of Chapter 4. As also discussed later, it is possible for increased densities to increase congestion, or at least the time required to complete trips, and lead to higher levels of noise and air pollution. More concentrated development may also contribute to the urban “heat island” effect resulting from the greater heat retention of urban surfaces, creating higher temperatures and electricity use (particularly for cooling) than characterize surrounding areas of more dispersed development; very compact development, however, may also limit the heat island effect if associated with a reduction in surface area covered with parking lots. This report focuses mainly on the effects of compact development on VMT, energy use, and CO2 emissions, although the wider benefits and costs are also noted.
Those seeking to address energy and climate change issues through land development strategies aimed at reducing VMT must also confront certain realities about the length of time necessary to affect VMT through changes in the built environment and the difficulties of making a substantial dent in petroleum imports in the near term. The
desirability of energy self-sufficiency in general is debatable; trade is beneficial for each partner because of the exploitation of comparative advantage.17 Moreover, the nation and the world are far from achieving consensus on how to share the burden of reducing GHG emissions. Nevertheless, as discussed later in the report, turnover of the housing stock over the next several decades provides opportunities for change that, along with the above-noted aging of the population and the arrival of new immigrants, may result in location and housing preferences for a greater number of compact developments than are in evidence today.
ORGANIZATION OF THE REPORT
The next two chapters are focused on the potential effects of land development policies on VMT—the first part of the committee’s charge. Chapter 2 describes trends in land development at the national and metropolitan area scales and also within metropolitan areas, particularly changes in population and employment densities and their implications for travel. Chapter 3 examines the empirical evidence on the relationship between the built environment and VMT by reviewing the enormous literature that has developed on the topic over the past two decades. Quantitative estimates of VMT reductions from more compact development are provided from the most reliable studies, but methodological and data problems hinder making more definitive statements about the magnitude of expected impacts.
The next two chapters are focused on the second part of the committee’s charge—estimating the potential future energy savings and reductions in CO2 emissions from more compact development. Chapter 4 helps set the stage by projecting how much new construction might be
expected in the coming decades to provide perspective on the numbers of residences and workplaces that could be influenced by more compact development strategies. Chapter 5 applies the results from the earlier chapters to develop scenarios for estimating the extent to which these strategies might reduce VMT and related energy consumption and CO2 emissions by 2030 and 2050. It examines the plausibility of reaching the development densities implicit in these scenarios, an area of disagreement among committee members. The chapter also considers other closely related benefits of more compact development, such as improved residential energy efficiency from increasing multifamily housing units or developing housing on smaller lots, as well as the costs of compact development. A final chapter presents the committee’s recommendations for policy and research.
BEA Bureau of Economic Analysis
FHWA Federal Highway Administration
IEA International Energy Agency
NRC National Research Council
NRCS National Resources Conservation Service
TRB Transportation Research Board
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