Considering Greenhouse Gas Emissions and Climate Change in Environmental Reviews: Conduct of Research Report (2024)

CHAPTER 5

Additional Research

The research findings suggest that the following additional research may be helpful to State DOTs to further enhance their ability to consider GHG emissions and climate change effects in environmental reviews.

• The most appropriate tools and methods for estimating GHG emissions associated with projects and mitigation strategies are increasingly well defined, with DOTs beginning to establish a set of typical practices. However, there is not yet an established body of practice for considering climate change effects in environmental review, or for considering equity related to climate change effects in the environmental review context. Support for DOTs to demonstrate best practices, and documentation of those practices, would be helpful.
• Related to estimation of GHG emissions, the largest uncertainty appears to be consideration of induced demand and the extent to which emissions increases from induced demand might offset the emission reduction benefits of improved traffic flow from capacity expansion or operational improvements. Additional research and case studies could be conducted using advanced modeling techniques to evaluate a variety of project types and contexts. This would be particularly helpful for agencies that lack the tools and/or resources to fully model induced demand effects and to support small- to medium-scale projects where in-depth modeling may not be practical or warranted.
• Many agencies interviewed for this study noted that they would appreciate more specific guidance on issues such as when to perform quantitative versus qualitative analysis, which tools and methods to use, and when to reference statewide or corridor-level programmatic assessments rather than performing project-level analysis (for both GHG emissions and climate change effects). These are policy questions more than research questions and are therefore issues that the U.S. DOT may choose to address through guidance.
• Sample assessments of the GHG emissions effects of roadway projects of different scales and contexts could support the development of programmatic assessments related to which types of projects require analysis versus which do not, or at least help to advise agencies on when effects might warrant quantitative analysis. For example, the Federal Transit Administration developed a programmatic analysis to report on whether certain types of proposed transit projects merit detailed analysis of GHG emissions at the project level and to be a source of data and analysis for FTA and its grantees to reference in future environmental documents for projects in which detailed, project-level GHG analysis is not vital (FTA, 2017).
• Similar programmatic assessments could potentially be developed for climate change effects. The ability to do this might depend on further research on the degree to which these effects and relevant conclusions are generalizable across similar projects or project contexts.

A separate memo documents implementation activities that can help to disseminate the guide and build capacity for its use.