The adverse effects of suburbanization and automobile dependence have long been evident but are currently of particular concern for several reasons. First, after decades of low energy prices, the cost of oil rose to record highs in 2008, reflecting the growth of China and India and the instability of many key suppliers in the Middle East and other oil-producing areas and underscoring U.S. dependence on imported fuels. The transportation sector as a whole accounts for more than 28 percent of annual U.S. energy consumption. Cars and light trucks, most of which are used for personal transportation, represent about 17 percent of that total, and this share has been rising. Second, concern about climate change continues to rise both domestically and internationally, and transportation is a major and increasing contributor to that growing problem. Gasoline consumption, largely by personal vehicles, accounts for about 20 percent of annual carbon dioxide (CO2) emissions, the largest single source of U.S. GHG emissions and the focus of the analyses conducted for this study. 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.

To examine the potential for reducing VMT, energy use, and CO2 emissions through more compact development, the committee formed to conduct this study commissioned five papers to augment its members’ expertise, received informational briefings at its early meetings, and performed a review of the literature. The committee’s findings and resulting recommendations are presented below. The committee reached consensus on all but one issue—the extent to which development is likely to become more compact by 2050 (see the text following Finding 4 for a detailed discussion).

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