The rapid increases in the speed, efficiency, and accessibility of the transportation system over the past century have enabled unprecedented levels of social interaction and economic productivity throughout the world. Transportation for personal mobility and for the movement of freight is integral to the high standard of living in developed nations and to fostering growth in developing nations.

Transportation activity, however, is a major user of the world’s carbon-rich fossil fuels and a major source of carbon dioxide (CO2) and other greenhouse gas (GHG) emissions associated with climate change. In the past 40 years, the developed world has mitigated many of the adverse environmental and public health impacts from transportation emissions—particularly in reducing the tailpipe pollutants from the burning of gasoline and diesel fuels.