The American Association of State Highway and Transportation Officials (AASHTO) has prepared this primer on transportation and climate change as an introduction to the issue of climate change and its implications for transportation policy in the United States. The primer summarizes the current state of scientific knowledge concerning the causes and impacts of climate change, outlines climate change policy issues, discusses trends and reviews potential measures in reducing greenhouse gas emissions from road transportation, and identifies issues for further research. Click here to view Section I, II, and III, and click here to view Section IV and V of this primer document.