The National Academies

NCHRP 25-64 [Completed]

Considering Greenhouse Gas Emissions and Climate Change in Environmental Reviews: Resources for State DOTs

  Project Data
Funds: $375,000
Research Agency: Cambridge Systematics, Inc.
Principal Investigator: Mr. Chris Porter
Effective Date: 7/27/2021
Completion Date: 1/26/2024
Comments: In publication process

According to the Environmental Protection Agency (EPA),​ greenhouse gas (GHG) emissions from transportation account for about 28 percent of total U.S. GHG emissions, making it the largest contributor of U.S. GHG emissions. In absolute terms, between 1990 and 2018, GHG emissions in the transportation sector increased more than any other sector  (https://www.epa.gov/transportation-air-pollution-and-climate-change/carbon-pollution-transportation). The climate-level processes affected by increased GHG emissions lead to changes that are experienced at the regional and local level. These include sea level rise, changes in precipitation regimes and temperature, and increases in the frequency or intensity of extreme weather events (e.g., hurricanes and heatwaves). These changes have important implications for public health and well-being, including increased heat-related deaths; damage and hazards from shoreline erosion and rural and urban flooding; impaired water quality from salt water intrusion in coastal areas; reduced air quality, whether from elevated levels of ozone due to warmer temperatures or particulate pollution from wildfires; and impacts on physical and mental health due to displacement and loss of life and property.
The negative impacts of climate change are disproportionately experienced by low-income neighborhoods and communities of color. Moreover, mitigating these impacts is a challenge as many of these same communities have, over time, experienced disinvestment that has left them with fewer resources for resilience to climate change impacts. Consideration of GHG emissions and climate change impacts is, therefore, a key component of conducting robust equity assessments and achieving environmental justice. Climate change impacts also affect natural habitats and public and private property, with implications for housing, manufacturing, agriculture, tourism, and government sectors.
On June 21, 2019, the Council on Environmental Quality (CEQ) issued the draft National Environmental Policy Act (NEPA) Guidance on Consideration of Greenhouse Gas Emissions (GHG) (84 FR 30097). This draft guidance follows the issuing (2016) and rescinding (2017) of past CEQ guidance. Although the outlook for federal regulatory requirements in this area remains uncertain, a number of state governments have adopted climate action plans and similar efforts to reduce GHG emissions and address climate change impacts. Apart from state and federal  policy directives or regulatory requirements, many communities are advocating for consideration of climate change and GHG emissions in transportation decision-making processes.
In response, many state DOTs are seeking ways to improve how  GHG emissions and climate change effects are addressed in environmental reviews, specifically the analysis and documentation required by National and State Environmental Policy Acts (NEPA and SEPA); Environmental Justice and equity analyses; Community Impact Assessment (CIA); or Planning and Environmental Linkages (PEL) studies. In addition, state DOTs can support statewide climate action plans or climate resilience initiatives by considering GHG emissions and climate change impacts of their projects and programs. For example, Texas DOT uses a programmatic statewide technical report for an on-road emissions analysis and climate change assessment to support environmental reviews for project development. 
Previous research has addressed methods for analyzing GHG emissions and climate change impacts that are potentially relevant for transportation decision-making. For example, the FHWA Infrastructure Carbon Estimator (ICE) 2.1, released in fall of 2020, estimates GHG emissions impacts of highway construction and operations using pre-engineering project information. NCHRP Project 25-56, "Methods for State DOTs to Reduce Greenhouse Gas Emissions from the Transportation Sector" (forthcoming 2021) is developing a guide to selecting GHG emissions tools for a wide range of decision-making applications and policy applications. While these projects provide examples and relevant background, they do not address the full range of considerations and approaches specific for environmental reviews. Further, emissions and energy models commonly used by transportation agencies to compare build alternatives typically indicate negligible changes in GHG emissions. At the same time, many climate change impacts stem from global processes and are indirect and/or cumulative in nature, which also makes them difficult to assess in connection with a specific project; the rescinded 2016 CEQ guidance addressed this issue through surrogate options for project-level analyses.
The objective of this research is to develop and pilot a handbook for state DOTs with resources and approaches for addressing GHG emissions and climate change impacts in environmental reviews. The handbook will include details on available methodologies and replicable examples that:
  • Use defensible methods
  • Clearly disclose impacts to communities and other stakeholders
  • Respond meaningfully to public comments and community concerns 
  • Inform mitigation efforts and transportation decision-making


In publication process.

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