It is generally accepted that the transportation sector of the economy contributes about 28% of the United States’ greenhouse gas emissions, making transportation a significant target of opportunity for mitigating strategies. Carbon dioxide is the major transportation-generated greenhouse gas, constituting over 80% of U.S. greenhouse gas emissions. Carbon dioxide emissions are directly linked to the amount of fuel consumed and its carbon intensity. Carbon emission reductions can be achieved by increasing the use of low-carbon fuels, improving fuel economy, reducing vehicle miles of travel, and reducing congestion. The job of a transportation analyst is to determine the cost effectiveness of various strategies at their disposal. This report provides background information to aid in understanding the issues, a summary of the state of the practice, a framework for conducting greenhouse gas analysis, a description of tools and data requirements, and an overview of the cost-effectiveness of various strategies. Eight short case studies are included to demonstrate the state of the practice by state departments of transportation, metropolitan planning organizations, and other units of government. Workshops were conducted in four states to vet the framework and the methods. The Practitioners Guide identifies steps in the transportation planning and environmental review process where greenhouse gas emissions could be considered and at what scale. The Practitioners Guide uses the decision points in the transportation planning and environmental review process from TCAPP to structure the information and link the scale of greenhouse gas analysis to stages in planning and environmental review. Finally the appendices to the Practitioners Guide contain data useful for conducting greenhouse gas emissions analysis, a compendium of tools, references to carbon calculators, life cycle fuel and emissions estimates and other resources. The report and Practitioners Guide provide a structure to aid transportation professionals in coping with the greenhouse gas emissions issue, clarify the types of mitigating actions available to a transportation agency, and provide methods and data for analysts. (Author/publisher)
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