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.
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