The design of communities and transportation systems is strongly related to nonmotorized transportation (NMT) behavior; however, the effect of environmental policy variables on total physical activity is not clear. Because large proportions of people in the United States live in the sprawling and exclusively residential environments associated with low levels of walking for transport, land use and transportation policies may already be having a substantial, although generally undocumented, impact on public health. Professionals from numerous fields are concerned that we have built our communities so that it is difficult, and in many cases dangerous, to walk or bike, and have thus "engineered" physical activity out of our daily lives. There is a public health imperative to evaluate environmental and policy variables and their associations with NMT, recreational physical activity, and total physical activity. The results of such studies can inform efforts to alter the environments in which people live their daily lives so as to promote population shifts in physical activity and improve transportation systems. Conducting and applying research on environmental correlates of NMT and physical activity will require collaboration among researchers from a wide range of professions.