Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Appendix A. Methodological
Issues
This Appendix provides a discussion of some key methodological issues
underlying the data and conclusions presented in this report, including:
• Criteria for inclusion of literature in this report—how the research team
determined which sources to use and cite;
• Basis for calculating greenhouse gas emission reductions;
• Treatment of cost-effectiveness—what is included and not included in the
cost and cost-effectiveness estimates;
• Analysis of life cycle emissions from fuels;
• Induced demand——the phenomenon of increased travel in response to
improvements in transportation conditions, which affects the reported
benefits of some of the system efficiency and travel activity strategies;
• Price elasticities and vehicle operating costs—the parameters used to
estimate the impacts of transportation system pricing measures; and
• The rebound effect—the extent to which increased travel (due to reduced
cost per mile of driving) may offset vehicle fuel efficiency gains.
Criteria for Inclusion of Literature in This Report
This report draws from over 400 references that provide information either
directly or indirectly related to the impact of transportation strategies on
greenhouse gas emissions. A broad range of literature is available on
transportation GHG emissions and related topics (such as vehicle travel
reduction, air pollutant emissions reduction, and energy savings), which is of
varying usefulness and validity. The research team that produced this report
applied its professional judgment to select studies that appear to have sound,
unbiased methodology and credible results. Sources include:
• Peer-reviewed academic articles published in journals or as conference
proceedings;
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