CHAPTER 1

Summary

Purpose of Project

The objective of National Cooperative Highway Research Program (NCHRP) Project 25-64, Considering Greenhouse Gas Emissions and Climate Change in Environmental Reviews: Resources for State DOTs, was to develop and pilot a guide for State departments of transportation (DOT) with resources and approaches for addressing greenhouse gas (GHG) emissions and climate change effects in environmental reviews. The guide is designed to help DOTs understand current requirements, guidance, practices, and available tools and methods to support consideration of GHG emissions and climate change effects in environmental reviews. These may include reviews conducted consistent with the National Environmental Policy Act (NEPA) as well as reviews conducted consistent with State environmental review requirements. The guide also discusses equity and environmental justice considerations and describes tools and methods for considering equity related to emissions and climate change effects.

Project Approach

The project team first reviewed current practice in addressing GHG emissions and climate change effects in environmental reviews, as well as environmental justice and equity considerations specific to those topics. The review considered Federal and State requirements and guidance, other relevant guidance and resources, and examples of environmental documents. The project team also reviewed available methodologies and tools for analyzing GHG emissions and climate change effects, and related equity effects, for transportation projects.

The project team then undertook various outreach and implementation activities to engage potential guide users and other stakeholders in development of the guide. These activities included: surveys and interviews with State DOTs on current practices and needs; surveys, interviews, and a workshop with nongovernmental organizations (NGO) and community-based organizations (CBO) known to have an interest in transportation GHG, climate, and/or equity issues; two peer exchanges with State DOTs, one focused on GHG emissions and one on climate change effects, to discuss current approaches and needs for additional guidance and resources; and pilot applications of the complete draft guide with two State DOTs, each including a series of three to five workshops focusing on various elements of the guide.

Key Findings

The review and outreach found that many State DOTs are working to incorporate the treatment of GHG emissions, climate change effects, or both in project planning and environmental reviews. There is a wide range of experience, with some States working hard to integrate all their activities (including environmental review) into unified, agencywide treatment of climate change while others just beginning their efforts. Many States recognized that they needed to develop or update their guidance but were waiting for finalization of Council on Environmental Quality (CEQ) guidance to do so (note that the outreach was conducted prior to release of interim CEQ guidance in January 2023).

The outreach found that the relevance of environmental review in the overall context of transportation planning may be increasingly limited as States shift resources from building capacity to maintaining a state of good repair. Many States prepare only a small number of environmental assessments (EA) and environmental impact statements (EIS). Furthermore, environmental analysis comes at the end of project planning and after key decisions have been made affecting GHG emissions and climate change effects. Considering these issues earlier, in transportation planning and programming, could support resource prioritization decisions with greater impacts on these considerations.

GHG emissions: States that have been quantifying GHG emissions have been converging on a relatively similar set of practices—often using the Federal Highway Administration (FHWA) mobile source air toxics (MSAT) guidance as an analog for determining analysis need and aligning analysis methods with MSAT analysis. Common tools include travel demand models, the Motor Vehicle Emission Simulator (MOVES) emission factor model, and the FHWA Infrastructure Carbon Estimator (ICE). The States thought that the existing tools for GHG emission analysis and addressing climate change effects were generally adequate but had some limitations, such as capturing mode shift or induced demand effects.

Climate change effects: Very few States have specific project-level written guidance or established approaches for addressing climate change effects in project environmental reviews, this does not mean the State DOTs have not been working on climate change effects. States are addressing climate change effects through statewide or planning-level studies. States have noted that tools to assess climate effects often fall short because 1) they contain dated information, 2) they are highly focused on one or another climate effect but not all, 3) they may not answer specific climate effect questions that are relevant to a project, and/or 4) they may be difficult to use.

Equity: States typically consider environmental justice in NEPA reviews consistent with FHWA and Federal Transit Administration (FTA) requirements and guidance, and in some cases with additional State requirements. Tools are available for identifying equity-focus communities and overlaying impacts. No States were identified that had developed guidance or procedures for addressing equity or environmental justice related to GHG emissions or climate change effects specifically within the context of environmental reviews, and no environmental documents were identified where an explicit linkage had been made.

Suggestions for 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.

• Establishing a body of practice for considering climate change effects in environmental review, and 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, 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.
• 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).
• Sample programmatic assessments to illustrate which types of projects may warrant quantitative GHG analysis versus which may not, as well as programmatic assessment approaches for climate change effects.