Sources and Resources for Planes, Trains, and Automobiles: Comparing the CO2 Impacts

U.S. National Transportation Statistics, Chapter 4, "Transportation, Energy, and the Environment," http://www.bts.gov/publications/national_transportation_statistics/#chapter_4

U.K. Department of Environment, Food, and Rural Affairs, "2008 Guidelines to Defra's GHG Conversion Factors: Methodology Paper for Transport Emission Factors," July 2008, http://www.defra.gov.uk/environment/business/envrp/pdf/passenger-transport.pdf

The Climate Registry, "General Reporting Protocol, Table 13.1 - U.S. Default CO2 Emission Factors for Transport Fuels," http://www.theclimateregistry.org/downloads/GRP.pdf