2.0 Summary

2.1 Objectives

This guide was developed to support state departments of transportation (DOTs) and partner agencies with resources and approaches for addressing greenhouse gas (GHG) emissions and climate change effects in transportation environmental reviews. Environmental reviews may be conducted for transportation projects pursuant to the National Environmental Policy Act (NEPA), as required for major federal actions. Some states may have their own environmental policies that provide additional requirements beyond those set forth under NEPA. This guide provides resources that are relevant to NEPA documentation but can also support states with additional requirements. Specifically, the guide is intended to help states:

  • Quantify GHG emissions when required by federal or state policy or leadership direction.
  • Use defensible methods to evaluate GHG emissions and incorporate available information on projected climate change effects in the project area.
  • Disclose project-related GHG emissions and climate change effects that could affect the project or the environment, providing clear information to communities and other stakeholders.
  • Respond meaningfully to public comments and community concerns.
  • Match tools with the project types, phases, and levels of analysis for which each tool is suited.
  • Identify strategies to reduce GHG emissions and measures to improve resilience to the projected effects of climate change (inform mitigation efforts).
  • Inform transportation decision-making.

The state of the practice for considering and addressing GHG emissions and climate change effects is rapidly evolving. The guide provides examples from practice throughout the U.S. but does not attempt to provide a single “recommended” practice or approach. Users of the guide should consider the examples presented here as illustrative of the state of practice when the guide was written (between 2021 and 2024) and should carefully consider their own state’s requirements and needs when developing a state-specific approach.

For purposes of this guide, “climate change effects” are defined to include:

  • Impacts to the completed project, such as more frequent or severe inundation and damage caused by sea level rise or coastal flooding.
  • Effects on travel, safety, the economy, etc. due to climate-related disruptions to the facility.
  • The project’s potential impact on the built and natural environments, to the degree that these impacts may be exacerbated by climate change.
  • Beneficial effects of a project to climate resilience.

2.2 Context of Climate Change

The environmental review process is an important aspect of transportation planning, facilitating agency decision-making and systematic consideration of project and program effects on the environment. Environmental reviews account for a wide range of factors that have the potential to impact the human and natural environment, as well as factors that affect the ability of a project to fulfill its purpose and need.

Reducing GHG emissions is increasingly urgent, with the effects of climate change already causing major damage locally and internationally. Limiting warming to 1.5°C above pre-industrial levels is regarded as the threshold needed to avoid the worst climate impacts (IPCC 2018). Current projections predict warming to surpass 2°C (IPCC 2021). As noted by the IPCC (2021), “Many changes in the climate system become larger in direct relation to increasing global warming. They include increases in the frequency and intensity of hot extremes, marine heatwaves, heavy precipitation, and, in some regions, agricultural and ecological droughts; an increase in the proportion of intense tropical cyclones; and reductions in Arctic sea ice, snow cover and permafrost.”

The GHG emissions of individual transportation projects are generally small as compared to national and global emissions. However, the transportation sector accounted for the largest share of the U.S. 2020 GHG emissions, at 27 percent (U.S. EPA 2022). Emission reduction goals, such as the federal goal of net-zero emissions by 2050 (U.S. DOS and EOP 2021), are aimed at reducing further exacerbation of climate change and its effects. Each decision made in the transportation sector can contribute to an increase or reduction in emissions, support or deter the achievement of broader climate and sustainability goals and contribute to building infrastructure that is more resilient or less resilient. Transportation agencies have the opportunity to contribute to making a more sustainable, resilient, and equitable transportation system through planning, programming, and project development, and can evaluate and document the effects of decisions through the associated environmental review processes.

2.3 Federal Policy and Guidance

NEPA requires that federal agencies take a hard look at the environmental effects of proposed actions. These environmental effects may include GHG emissions and climate change effects. Federal guidance on considering GHG emissions and climate change effects has existed (at least in publicly available draft form) since 2010 and has continued to evolve with the changing priorities of different presidential administrations. In 2016, the Council on Environmental Quality (CEQ) issued its Final Guidance for Federal Departments and Agencies on Consideration of Greenhouse Gas Emissions and the Effects of Climate Change in National Environmental Policy Act Reviews (CEQ 2016). While this guidance was withdrawn in 2017, Executive Order 13990 directed CEQ to review, for revision and update, the 2016 guidance and, in the interim, recommended its consideration (EOP 2021a). The interim National Environmental Policy Act Guidance on Consideration of Greenhouse Gas Emissions and Climate Change was released in January 2023 (CEQ 2023a). In July 2023, CEQ issued a proposed rule to revise NEPA implementing regulations (CEQ 2023b). The proposed changes include codifying consideration of climate change. The 2023 CEQ guidance provides more specificity than past guidance related to consideration of GHG emissions but does not require the use of specific tools or methods.

Key Provisions of 2023 CEQ Guidance (CEQ 2023a; CEQ 2023b)

  • GHG emissions effects should be quantified if possible; if quantification is not possible, a range of emissions should be estimated; otherwise effects may be described qualitatively. As with any NEPA analysis, the level of effort for GHG emissions analysis should be proportionate to the scale of the emissions relevant to the NEPA review.
  • Available assessments and scenarios should be used to consider climate change effects; it is not necessary for agencies to conduct new research or analysis of potential impacts of climate change on the project area.
  • The NEPA reviews for a specific action can incorporate by reference earlier programmatic studies or information such as management plans, inventories, assessments, etc.

Federal direction on environmental justice was first established in the 1990s. Guidance from federal agencies, including U.S. DOT and modal administrations, has continued to evolve since that time. Until recently, there has been no specific guidance on addressing the linkages between GHGs or climate impacts and environmental justice. In 2021, the administration at the time established the Justice40 Initiative, which set a goal to deliver at least 40 percent of the overall benefits from federal investments in climate and clean energy to disadvantaged communities, and began developing guidance for considering equity under this initiative. The 2023 CEQ guidance places a strong emphasis on incorporating environmental justice considerations into analyses of climate-related effects.

2.4 State Policy and Guidance

Since federal guidance on considering GHG emissions and climate change effects in NEPA reviews has only been formally in place for a short period of time, states that have already considered these issues have done so largely for other reasons: in anticipation of the adoption of federal requirements or guidance; because of state or agency directives or policy to consider these effects; in response to state legislation that addresses climate change, either through Climate Action Plans or specified emission reduction targets; or in direct response to public and stakeholder interest. As of 2021, at least 11 state DOTs had adopted written guidance on addressing GHG emissions and/or climate change effects in federally or state-required transportation project environmental review, mainly focusing on GHG emissions. The range of approaches varies from purely qualitative (including referencing to statewide assessments), to requirements for quantitative GHG analysis for projects meeting certain criteria (e.g., when an Environmental Impact Statement or Environmental Assessment is conducted). Other states may have informal policies or no policies at all, considering GHG emissions and climate change effects on a project-by-project basis.

2.5 Recent Practices

The consideration of GHG emissions in environmental reviews, including quantitative assessment, has increased over the past decade. Quantitative assessments typically use the U.S. Environmental Protection Agency Motor Vehicle Emission Simulator (MOVES) model, in conjunction with traffic forecasts, to estimate traffic-generated GHG emissions under base year, future no-build, and one or more build alternatives. Some states have aligned their practices with the Federal Highway Administration (FHWA) guidance for evaluating mobile source air toxics. The FHWA Infrastructure Carbon Estimator has been used to estimate emissions related to construction, maintenance, and operational activities. Other tools and data have been used in a few examples to estimate emissions associated with transit operations, electricity, and upstream or “fuel cycle” emissions.

Consideration of climate change effects also appears to be increasing and becoming more robust. However, a typical or standard approach to evaluating climate change effects has not yet been developed.

To date, there have been few or no instances of linking GHG, climate, and equity in environmental documentation. Environmental justice concerns are typically addressed in environmental reviews pursuant to federal requirements and guidance. Outreach to environmental justice communities and analysis of equity effects could readily be expanded to include GHG emissions and climate change effects. In 2022, the CEQ developed the Climate and Economic Justice Screening Tool as a step in implementing President Biden’s Justice40 Initiative. The tool is intended to help agencies identify disadvantaged communities that will benefit from programs included in the Justice40 Initiative.

Practitioners have found it challenging to draw conclusions regarding GHG and/or climate change effects, especially when there is no guidance about what scale of effects might be considered significant. Most project documents that consider GHG emissions have concluded either that emissions would be reduced or that emissions effects would be insignificant in proportion to statewide, national, or global emissions (an approach that CEQ and EPA discourage) or that other agency or sectoral efforts to reduce emissions would eventually address the problem or that no conclusions can be reached given the lack of guidance on significance. Instead of making a conclusion on impact significance based solely on the magnitude of project-related emissions, some projects draw conclusions based on the project’s consistency with broader local or statewide climate goals. Many factors are typically considered when selecting a preferred project alternative, and GHG emissions and climate change effects may be among those factors.

Stakeholders have commented that many of the key decisions influencing GHG emissions and climate change effects are made earlier in the process than environmental review (e.g., long-range planning and programming). Some agencies have therefore chosen to mainly address GHG emissions and/or climate change effects at the programmatic level, e.g., by developing climate action plans, funding GHG-reducing projects, conducting system-wide vulnerability assessments, and revising design standards to increase climate resilience. The 2023 CEQ interim guidance states that programmatic assessments may be referenced to support project-level environmental documentation (CEQ 2023a).

2.6 Advancing State Policy and Practice

Transportation agencies typically will have an established set of policies and procedures for conducting environmental review for projects, consistent with federal and any applicable state regulations and guidelines. Consideration of GHG emissions and climate change effects can be integrated within these policies and procedures. A potential template for developing a standard agency approach to considering GHG emissions and climate change effects in environmental reviews might include the following steps.

  • Establish intra-agency coordination procedures such as joint meetings between environmental, planning, project development, and sustainability or climate change staff.
  • Review programmatic or systems-level GHG and vulnerability assessments conducted by the agency, and consider how these might be undertaken, expanded, or referenced to support project-level assessment.
  • Review project development procedures and consider steps that could be taken to better incorporate GHG emissions and/or climate effects beginning in the early phases.
  • Include GHG and climate change considerations in Categorical Exclusion checklists.
  • Identify existing procedures, tools, and methods for considering GHG emissions and climate change effects, including equity effects, and define how those could be directly used or enhanced to support environmental analysis.
  • Develop a menu of GHG emission mitigation options and resilience strategies to be considered at the project level, as well as a process to work with design teams early on to ensure that practicable and compatible mitigation and resilience measures are developed and implemented.
  • Solicit input from partner agencies and stakeholder groups on what changes the agency should make to better consider and address GHG emissions and climate change effects associated with projects.
  • Create a draft set of policies, procedures, and technical methods for considering GHG emissions and climate change effects, test them on real or hypothetical projects, share for feedback, and finalize.
  • Develop a communications and training program to inform relevant agency staff, the consultant community, and the public (including environmental justice communities and Tribal Nations) of the policies and procedures.
  • Revisit policies and procedures after a few years of application to determine how well they are working, including level of effort and the value of information they are providing to inform decision-making, and for alignment with any recent changes to federal or state legislation policies.

2.7 How to Use This Guide

Section 3.0 of this guide provides background information on environmental review procedures, requirements, and guidance. It first describes how environmental review relates to transportation planning and project development activities. It then provides an overview of relevant federal environmental review policy and guidance, including those related to equity considerations, and discusses state environmental review procedures. It concludes with an overview of current practice by state transportation agencies and a summary of feedback on the state of practice as obtained from various stakeholder groups.

Section 4.0 provides an in-depth look at how GHG emissions can be considered in environmental review. It describes approaches for both planning-level and project-level assessment, provides information on analysis tools and methods, discusses equity considerations, provides examples of how findings can be communicated and conclusions drawn, and discusses mitigation measures. It also describes how project or plan-level GHG assessment might relate to statewide GHG reduction goals or targets, and includes examples of practice.

Section 5.0 provides an in-depth look at how climate change effects can be considered in environmental review. It identifies potential effects that may be considered; describes how programmatic assessments can inform project-level assessment; provides information on analysis tools and methods; discusses equity considerations; provides examples of how findings can be communicated and conclusions drawn; and discusses mitigation measures. It also provides examples from practice.

Section 6.0 discusses implementation, with a focus on challenges and potential solutions.

Appendix A: Annotated Bibliography provides an annotated bibliography of all the references in this guide.

Appendix B: Tools to Support Evaluation of GHG Emissions, Climate Effects, and Equity provides a spreadsheet of tables with detailed information on tools available to support evaluation of GHG emissions, climate change effects, and equity related to climate effects.

Appendix C: Review of EIS Documents provides a spreadsheet with information from a detailed review of 21 environmental documents on how GHG emissions and climate change effects were addressed in these documents.

Appendix D: Sample Approach for Considering Greenhouse Gas Emissions and Climate Change Effects in Environmental Reviews provides a sample approach for considering greenhouse gas emissions and climate change effects in environmental reviews, based on materials developed for the pilot workshops.

Appendix E provides a list of definitions of terms used in the guide, along with a table of abbreviations and acronyms that appear in the guide.