Based on a comprehensive study review by leading urban planning researchers, this investigative document demonstrates how urban development is both a key contributor to climate change and an essential factor in combating it—by reducing vehicle greenhouse gas emissions.
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About the Author
Reid Ewing is a research professor at the National Center for Smart Growth at the University of Maryland. He lives in College Park, Maryland. Keith Bartholomew is an assistant professor of urban planning at the University of Utah's College of Architecture + Planning. Steve Winkelman is the director of the Transportation Program at the Center for Clean Air Policy. Jerry Walters is a principal and chief technical officer with Fehr & Peers Associates, a California-based transportation planning and engineering firm. Don Chen is the founder and executive director of Smart Growth America.
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Evidence on Urban Development and Climate Change
By Reid Ewing, Keith Bartholomew, Steve Winkelman, Jerry Walters, Don Chen
Urban Land InstituteCopyright © 2008 ULI-the Urban Land Institute
All rights reserved.
The phrase "you can't get there from here" has a new application. For climate stabilization, a commonly accepted target for the year 2050 would require the United States to cut its carbon dioxide (CO2) emissions by 60 to 80 percent below 1990 levels. Carbon dioxide levels have been increasing rapidly since 1990, and so would have to level off and decline even more rapidly to reach this target level by 2050. This publication demonstrates that the U.S. transportation sector cannot do its fair share to meet this target through vehicle and fuel technology alone. We have to find a way to sharply reduce the growth in vehicle miles driven across the nation's sprawling urban areas, reversing trends that go back decades.
This publication is based on an exhaustive review of existing research on the relationship among urban development, travel, and the CO2 emitted by motor vehicles. It provides evidence on and insights into how much CO2 savings can be expected with compact development, how compact development is likely to be received by consumers, and what policy changes will make compact development possible. Several related issues are not fully examined in this publication. These include the energy savings from more efficient building types, the value of preserved forests as carbon sinks, and the effectiveness of pricing strategies — such as tolls, parking charges, and mileage-based fees — when used in conjunction with compact development and expanded transportation alternatives.
The term "compact development" does not imply high-rise or even uniformly high density, but rather higher average "blended" densities. Compact development also features a mix of land uses, development of strong population and employment centers, interconnection of streets, and the design of structures and spaces at a human scale.
Scientific consensus now exists that greenhouse gas accumulations due to human activities are contributing to global warming with potentially catastrophic consequences (IPCC 2007). International and domestic climate policy discussions have gravitated toward the goal of limiting the temperature increase to 2ºC to 3ºC by cutting greenhouse gas emissions by 60 to 80 percent below 1990 levels. The primary greenhouse gas is carbon dioxide, and every gallon of gasoline burned produces about 20 pounds of CO2.
Driving Up CO2 Emissions
The United States is the largest emitter worldwide of the greenhouse gases (GHGs) that cause global warming. Transportation accounts for a full third of CO2 emissions in the United States, and that share is growing, rising from 31 percent in 1990 to 33 percent today. It is hard to envision a "solution" to the global warming crisis that does not involve slowing the growth of transportation CO2 emissions in the United States.
The Three-Legged Stool Needed to Reduce CO2 from Automobiles
Transportation CO2 reduction can be viewed as a three-legged stool, with one leg related to vehicle fuel economy, a second to the carbon content of the fuel itself, and a third to the amount of driving or vehicle miles traveled (VMT). Energy and climate policy initiatives at the federal and state levels have pinned their hopes on shoring up the first two legs of the stool, through the development of more efficient vehicles (such as hybrid cars) and lower-carbon fuels (such as biodiesel fuel). Yet a stool cannot stand on only two legs.
As the research compiled in this publication makes clear, technological improvements in vehicles and fuels are likely to be offset by continuing, robust growth in VMT. Since 1980, the number of miles Americans drive has grown three times faster than the U.S. population, and almost twice as fast as vehicle registrations (see Figure 1–1). Average automobile commute times in metropolitan areas have risen steadily over the decades, and many Americans now spend more time commuting than they do vacationing.
This raises some questions, which this report addresses. Why do we drive so much? Why is the total distance we drive growing so rapidly? And what can be done to alter this trend in a manner that is effective, fair, and economically benign?
The growth in driving is due in large part to urban development, or what some refer to as the built environment. Americans drive so much because we have given ourselves little alternative. For 60 years, we have built homes ever farther from workplaces, located schools far from the neighborhoods they serve, and isolated other destinations — such as shopping — from work and home. From World War II until very recently, nearly all new development has been planned and built on the assumption that people will use cars every time they travel. As a larger and larger share of our built environment has become automobile dependent, car trips and distances have increased, and walking and public transit use have declined. Population growth has been responsible for only a quarter of the increase in vehicle miles driven over the last couple of decades. A larger share of the increase can be traced to the effects of a changing built environment, namely to longer trips and people driving alone.
As with driving, land is being consumed for development at a rate almost three times faster than population growth. This expansive development has caused CO emissions from cars to rise even as it has reduced the amount of forest land available to absorb CO2.
How Growth in Driving Cancels Out Improved Vehicle Fuel Economy
Conventional pollutants can be reduced in automobile exhaust with sophisticated emission control systems such as catalytic converters, on-board computers, and oxygen sensors. In contrast, CO2 is a fundamental end product of burning fossil fuels; there is no practical way to remove or capture it from moving vehicles. At this point in time, the only way to reduce CO2 emissions from vehicles is to burn less gasoline and diesel fuel.
An analysis by Steve Winkelman of the Center for Clean Air Policy, one of the coauthors of this publication, finds that CO2 emissions will continue to rise, despite technological advances, as the growth in driving is projected to overwhelm planned improvements in vehicle efficiency and fuel carbon content from the Energy Independence and Security Act of 2007 (U.S. Congress 2007). The act requires passenger vehicle fuel economy improvements to at least 35 miles per gallon (mpg) for new passenger vehicles by 2020, which would lead to a 34 percent increase in fleet-wide fuel economy by 2030 (green line in Figure 1–2). The act also sets renewable fuel requirements that Winkelman calculates would reduce lifecycle GHG emissions by 10 percent by 2025 (purple line). Absent growth in driving, these measures would reduce CO emissions from cars and light trucks by 23 percent below current levels.
Even when these more stringent standards for vehicles and fuels fully penetrate the market, however, transportation-related emissions still would far exceed target levels for stabilizing the global climate. The U.S. Department of Energy's Energy Information Administration (EIA) forecasts a 48 percent increase in driving between 2005 and 2030 (orange line in Figure 1–2), outpacing the projected 23 percent increase in population (EIA 2008). The rapid increase in driving would overwhelm both the increase in vehicle fuel economy and the lower carbon fuel content required by the Energy Independence and Security Act of 2007. Carbon dioxide emissions from cars and light trucks would remain at 2005 levels (blue line), or 26 percent above 1990 levels (light blue line) in 2030. For climate stabilization, the United States must bring the CO2 level to approximately 33 percent below 1990 levels by 2030 to be on a path to a CO reduction of 60 to 80 percent by 2050 (red line).
As the projections show, the United States cannot achieve such large reductions in transportation-related CO2 emissions without sharply reducing the growth in the number of miles driven.
Changing Development Patterns to Slow Global Warming
Recognizing the unsustainable growth in driving, the American Association of State Highway and Transportation Officials (AASHTO), representing state departments of transportation, is urging that the growth of vehicle miles driven be cut in half. How does a growing country — one with 300 million residents and another 120 million on the way by mid-century — slow the growth of vehicle miles driven? Aggressive measures certainly are available, including imposing ever stiffer fees and taxes on driving and parking or establishing no-drive zones or days. Some countries are experimenting with such measures. However, many in this country would view these measures as punitive, given the reality that most Americans do not have a viable alternative to driving. The body of research surveyed here shows that much of the rise in vehicle emissions can be curbed simply by growing in a way that will make it easier for Americans to drive less. In fact, the weight of the evidence shows that, with more compact development, people drive 20 to 40 percent less, at minimal or reduced cost, while reaping other fiscal and health benefits.
How Compact Development Helps Reduce the Need to Drive
Better community planning and more compact development help people live within walking or bicycling distance of some of the destinations they need to get to every day — work, shops, schools, and parks, as well as transit stops. If they choose to use a car, trips are short. Rather than building single-use subdivisions or office parks, communities can plan mixed-use developments that put housing within reach of these other destinations. The street network can be designed to interconnect, rather than end in culs-de-sac and funnel traffic onto overused arterial roads. Individual streets can be designed to be "complete," with safe and convenient places to walk, bicycle, and wait for the bus. Finally, by building more homes as condominiums, townhouses, or detached houses on smaller lots, and by building offices, stores and other destinations "up" rather than "out," communities can shorten distances between destinations. This makes neighborhood stores more economically viable, allows more frequent and convenient transit service, and helps shorten car trips.
This type of development, which has seen a resurgence in recent years, goes by many names, including "walkable communities," "new urbanist neighborhoods," and "transit-oriented developments" (TODs). "Infill" and "brownfield" developments put unused parcels in urban areas to new uses, taking advantage of existing infrastructure and nearby destinations. Some "lifestyle centers" are now replacing single-use shopping malls with open-air shopping on connected streets with housing and office space above stores. And many communities have rediscovered and revitalized their traditional town centers and downtowns, often adding more housing to the mix. These varied development types are collectively referred to in this publication as "compact development" or "smart growth."
How We Know That Compact Development Will Make a Difference: The Evidence
As these forms of development have become more common, planning researchers and practitioners have documented the fact that residents of compact, mixed-use, transit-served communities drive less than their counterparts in sprawling communities. Studies have looked at the issue from varying angles. They have:
* compared travel statistics for regions and neighborhoods of varying compactness and auto orientation;
* analyzed the travel behavior of individual households in various settings; and
* simulated the effects on travel of different future development scenarios at the regional and project scales.
Regardless of the approach, researchers have found significant potential for compact development to reduce the miles that residents drive.
A comprehensive sprawl index developed by coauthor Reid Ewing of the National Center for Smart Growth at the University of Maryland ranked 83 of the largest metropolitan areas in the United States by their degree of sprawl, measured in terms of population and employment density, mix of land uses, strength of activity centers, and connectedness of the street network (Ewing, Pendall, and Chen 2002, 2003). Even accounting for income and other socioeconomic differences, residents drove about 25 percent less in the more compact regions. In sprawling Atlanta and Raleigh, residents racked up more than 30 miles driving each day for every person living in the region. In more compact Boston and Portland, Oregon, residents drove less than 24 miles per person per day.
This finding holds up in studies that focus on the travel habits of individual households. The link between urban development patterns and individual or household travel has become the most heavily researched subject in urban planning, with more than 100 rigorous empirical studies completed. These studies have been able to account for factors such as the tendency of higher-income households to make more and longer trips than lower-income families.
One of the most comprehensive studies, conducted in King County, Washington, by Larry Frank of the University of British Columbia (Frank, Kavage, and Appleyard 2007), found that residents of the most walkable neighborhoods drive 26 percent fewer miles per day than those living in the most sprawling areas. A meta-analysis of many of these types of studies shows that people living in places with twice the density, diversity of uses, accessible destinations, and interconnected streets drive about a third less than otherwise comparable residents of low-density sprawl.
Many studies have been conducted by or in partnership with public health researchers interested in how the built environment can be better designed to encourage daily physical activity. These studies show that residents of communities designed to be walkable both drive fewer miles and also make more trips by foot and bicycle, which improves individual health. A recent literature review found that 17 of 20 studies, all dating from 2002 or later, have established statistically significant links between some aspect of the built environment and obesity.
Two other types of studies also find strong associations between development patterns and driving: simulations that predict the impacts of various growth options for entire regions and simulations that predict the impacts of individual development projects when sited and designed in different ways. In regional growth simulations, planners compare the effect of a metropolitan-wide business-as-usual scenario with more compact growth options. Coauthor Keith Bartholomew of the University of Utah analyzed 23 of these studies and found that compact scenarios generate up to one-third fewer miles driven than business-as-usual scenarios (Bartholomew 2005, 2007). The better-performing scenarios are those with higher degrees of land use mixing, infill development, and population density, as well as a larger amount of expected growth. Under a plausible set of assumptions, the reduction of miles driven with compact development would be 18 percent by 2050. Even this may be on the low side, since the travel models used in these studies only crudely account for travel within neighborhoods and disregard walk and bike trips entirely.
Atlantic Station today.
Of the project-level studies, one of the best known evaluated the impact of building a very dense, mixed-use development at an abandoned steel mill site in the heart of Atlanta versus spreading the equivalent amount of commercial space and number of housing units in the prevailing patterns at three suburban locations. Analysis using travel models enhanced by coauthor Jerry Walters of Fehr & Peers Associates (Walters, Ewing, and Allen 2000), and supplemented by the U.S. Environmental Protection Agency's Smart Growth Index (to capture the effects of site design) found that the infill location would generate about 36 percent less driving and emissions than the outlying comparison sites. The results were so compelling that the development was deemed a transportation control measure by the federal government for the purpose of improving the region's air quality.
The Atlantic Station project in Midtown Atlanta has become a highly successful reuse of central city industrial land. An early evaluation of travel by residents and employees of Atlantic Station suggests even larger VMT reductions than projected originally. On average, Atlantic Station residents are estimated to generate eight VMT per day, and employees to generate 11 VMT per day. These estimates compare favorably with a regional average VMT of more than 32 miles per person per day, among the highest in the nation.
The Potential of Smart Growth
The potential of smart growth to curb the rise in GHG emissions will, of course, be limited by the amount of new development and redevelopment that takes place over the next few decades, and by the share of it that is compact in nature. A great deal of new building will take place as the U.S. population grows to 420 million in 2050. According to the best available analysis, by Arthur "Chris" Nelson of Virginia Tech, 89 million new or replaced homes — and 190 billion square feet of new offices, institutions, stores, and other nonresidential buildings — will be constructed through 2050. If Nelson's forecasts are correct, two-thirds of the development on the ground in 2050 will be built between 2007 and then. Pursuing smart growth is a low-cost climate change strategy, because it involves shifting investments that have to be made anyway.
Excerpted from Growing Cooler by Reid Ewing, Keith Bartholomew, Steve Winkelman, Jerry Walters, Don Chen. Copyright © 2008 ULI-the Urban Land Institute. Excerpted by permission of Urban Land Institute.
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Table of Contents
ContentsCHAPTER 1 Overview,
CHAPTER 2 Emerging Trends in Planning, Development, and Climate Change,
CHAPTER 3 The VMT/CO2/Climate Connection,
CHAPTER 4 The Urban Environment/VMT Connection,
CHAPTER 5 Environmental Determinism versus Self Selection,
CHAPTER 6 Induced Traffic and Induced Development,
CHAPTER 7 The Residential Sector,
CHAPTER 8 The Combined Effect of Compact Development, Transportation Investments, and Road Pricing,
CHAPTER 9 Policy and Program Recommendations,
CHAPTER 10 Conclusion,
Related ULI Publications,