Assessment of Greenhouse Gas Analysis Techniques for Transportation Projects

The transportation sector is one the fastest growing sources of greenhouse gas (GHG) emissions, accounting for 28 percent of national emissions in 2005. As states and local governments attempt to reduce emissions of GHGs that contribute to climate change, they are increasingly interested in understanding the linkages between transportation activities and GHG emissions. Because there are no regulations addressing GHG emissions from transportation sources – California being the notable exception – state departments of transportation (DOTs), metropolitan planning organizations (MPOs), and other transportation agencies have limited experience analyzing the GHG emissions impacts of transportation plans and projects. Developing credible baseline information is a critical first step in addressing GHG emissions from transportation activities at any level. Policymakers and planners may also be unfamiliar with available tools and techniques to facilitate analyses of GHG impacts for various policy options. Moreover, some transportation agencies are concerned that the available techniques may not be sufficient to conduct the types of analyses necessary to strategically address GHG emissions at the project, local, and regional levels. This paper summarizes the findings of a recent project for the National Cooperative Highway Research Program (NCHRP) that involved identification and review of 17 tools or methods available to analyze the GHG implications of transportation projects. It identifies the tools most suitable for four kinds of transportation/GHG analyses: state-level transportation GHG inventory development; state-level transportation GHG inventory projections; regional transportation plan or program analysis; and transportation project and strategy-specific analyses. In addition, this paper summarizes the gaps identified in existing methodologies.