This document calls for major improvements to the United States transportation infrastructure. The vision includes improvements in energy independence, environmental compatibility, safety, cost, and performance.

The degree to which carbon flows balance each other - human activities leading to carbon emissions into the atmosphere, vegetation and oceans soaking it up - is the subject of vigorous debate. It is not yet possible to define quantitatively the global effects of human activities such as forestry and agriculture, and may never be so. However, studies to determine these effects have emerged as critical for understanding how the earth's climate will evolve in the future. Global concern about the potential implications of the behaviour of the carbon cycle under anthropogenic stress includes concepts of system instability and large scale change. To contribute to understanding this behaviour, and our potential responses to it, requires a thorough investigation of both biophysical and social systems. Until recently, most scientific assessments of such risks focused on the anatomy of conceivable environmental changes themselves, devoting little attention to either the human driving forces or the ecosystems and societies that might be endangered by the changes. Recently, however, questions about the linkage and interaction of social, ecological, and biogeochemical systems are emerging as a central focus of policy-driven assessments of global environmental risks. The approach used here is to accept humans as an integral …