Increases in per capita vehicle usage and associated emissions have spawned an increased examination of the ways in which our communities and regions are developing. Associated with increased vehicle usage are decreased levels of walking and biking, two valid forms of physical activity. The Surgeon General's 1996 report, Physical Activity and Health, highlights the increasing level of physical inactivity as a growing cause of mortality. The costs and benefits of contrasting land development and transportation investment practices have been the subject of considerable debate in the literature. Findings have been refuted based on methodological grounds and inaccurate interpretation of data. Several of these studies, their methodological approaches, and their critiques are analyzed. While most agree that the built environment influences travel, considerable disagreement exists over the likely impacts of increased density, mix, and street connectivity on air quality, and on transportation system performance and household activity patterns.
