Providing safe, convenient places for walking and bicycling can reduce barriers to participating in regular physical activity. We examined bicycle- and pedestrian-related investments authorized by federal transportation legislation in 3,140 counties in the United States by region, population size and urbanization, social and economic characteristics, and indicators of travel-related walking and bicycling. From 1992 to 2004, states and counties implemented 10,012 bicycle- and pedestrian-related projects representing $3.17 billion in federal expenditures. We found disparities in implementation and system-building outcomes according to population size and location and social and economic indicators. Counties characterized by persistent poverty (odds ratio=0.69, 95% confidence interval 0.53-0.91) or low educational status (odds ratio=0.66, 95% confidence interval 0.52-0.84) were less likely to implement projects. Three key policy recommendations for improving public health outcomes are drawn from this research: Improved data tracking, more explicit linkages between transportation projects and public health, and improved planning assistance to underserved communities are all seen as essential steps.