State DOT decarbonization research thus far

NCHRP 25-25/Task 115 [Active]

Estimates of Emissions Reductions from Future Fleet Changes for Use in Air Quality Models
NCHRP 25-25 (Research for the AASHTO Committee on Environment and Sustainability) ]


  Project Data
Funds: $125,000
Staff Responsibility: Ann M. Hartell
Research Agency: Louis Berger U.S. Inc. & Sonoma Technology Inc.
Principal Investigator: Dr. Song Bai
Effective Date: 12/1/2018
Completion Date: 11/30/2019


Early implementation of new vehicle technologies and publicly sponsored programs, which are anticipated to reduce vehicle emissions, is underway in the United States. These technologies include electric and fuel cell vehicles and improvements for these vehicle types such as enhanced battery storage capacity that extend the range of electric vehicles. Interest in these zero-emission vehicles (ZEVs) extends to freight and commercial operators (e.g. Tesla’s Semi truck, Toyota’s fuel cell semi truck, green vehicle taxi fleets). Further, most connected and automated vehicles are anticipated to be electric. Federal, state, and local programs, such as FHWA’s Alternative Fuels Corridor Program, encourage the adoption of ZEVs.

It is reasonable to assume that ZEVs will have a role in reducing mobile source emissions. Depending on the rate of adoption of these technologies and the timing of related program implementation, the reduction in vehicle emissions may be faster than assumed in state and regional plan documents; such an acceleration could benefit areas designated as nonattainment or maintenance areas for one or more pollutants.

Evaluating the potential emission reduction impacts from ZEVs and related programs may assist state departments of transportation (DOTs) and Metropolitan Planning Organizations (MPOs) in their efforts to develop plans and programs to control mobile source emissions. To do so, state DOTs and MPOs need robust and plausible estimates of projected emissions reductions to inform plans, programs, and policies to increase air quality benefits resulting from the adoption of these technologies.


The objective of this research is to develop projected changes in emissions of criteria pollutants, mobile source air toxic pollutants (MSATs), and greenhouse gases (GHGs) resulting from varying adoption rates of ZEVs based upon a set of plausible scenarios with a 20-year time horizon.

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NCHRP 25-56 [Active]

Methods for State DOTs to Reduce Greenhouse Gas Emissions from the Transportation Sector

  Project Data
Funds: $600,000
Includes $250,000 from the Federal Highway Administration (FHWA)
Research Agency: Cambridge Systematics
Principal Investigator: Mr. Chris Porter
Effective Date: 5/1/2018
Completion Date: 10/31/2020
Many methods and tools are available to measure GHG emissions and to evaluate expected GHG emissions reductions from transportation-related strategies. Despite the availability of methods, state DOTs face challenges to the integration of these methods into their planning and programming processes, including limited funding, incomplete data, lack of staff capacity, absence of strong incentives, and the addition of another layer of analysis to an already complex transportation decision-making process. These challenges make it difficult for state DOTs to develop and manage the transportation system in a way that will reduce GHG emissions, and to document changes in GHG emissions from the transportation sector.
Selecting appropriate methods requires matching the needs and decision-making context of a state DOT with the characteristics of the method. Some state DOTs have adopted a method to evaluate GHG emissions reductions, yet struggle to link it with planning and programming decisions. State DOTs mandated to reduce GHG emissions from the transportation sector need a robust method to evaluate reductions that provides clear direction for selecting effective transportation strategies and defensible estimates of expected impacts on emissions while accounting for confounding factors and uncertainty. Other states may be interested in methods to calculate cost-effectiveness of transportation strategies in reducing GHG emissions.
In addition to decisions under the purview of a state DOT, there are other ways to reduce GHG emissions, many of which are spearheaded by other entities. For example, a local jurisdiction may adopt a land use development plan driven by a GHG emissions reduction goal. The plan may include strategies to create walkable and bikeable neighborhoods, compact employment centers, and multimodal corridors. The design and operation of the transportation network is an important part of achieving such goals; therefore a state DOT can be a vital partner in implementing such a plan and supporting progress toward local planning goals. Yet because state DOT planning and programming processes can be isolated from local planning and development decisions, state DOT decisions may erode progress toward a local GHG emissions reduction goal. To be effective partners, state DOTs need GHG emissions evaluation methods appropriate for use with partners and for collaboration across jurisdictional scales and sectoral boundaries.
Guidance on GHG emissions reduction strategies for state DOTs was developed under the second Strategic Highway Research Program (SHRP2) Capacity Project C09, titled Incorporating Greenhouse Gas Emissions into the Collaborative Decision-Making Process ( practitioner guide and accompanying research report include information on GHG-reducing transportation strategies and a technical framework for assessing baseline GHG emissions and the effects of potential projects and strategies. The technical information was accompanied by a series of case studies of state DOT and metropolitan planning organization (MPO) efforts to assess GHG emissions in planning and project development. Although the SHRP2 project provided considerable detail on available methods, implementation of the framework has been limited.
Since the SHRP2 effort, new methods and tools have been developed. Among these is FHWA’s Energy and Emissions Reduction Policy Analysis Tool (EERPAT), which evaluates the energy implications of a wide variety of policy options at the state or county level. Currently available methods vary considerably in their level of detail, data requirements, rigor, and applicability to state DOT planning and programming decisions. Selecting a method to evaluate GHG emissions reductions requires understanding the appropriateness of the method for the decision-making context, identifying opportunities to integrate GHG considerations into the decision-making process, as well as gaining leadership support and building organizational capacity to apply the method. Technical issues including data availability must also be resolved.
This project will build upon the existing body of research and recent state DOT experience to develop updated guidance on methods to evaluate transportation strategies for their capacity to reduce GHG emissions and how to integrate these methods into state DOT planning and programming processes.


The objective of this project is to provide guidance on currently available, practical, and innovative methods for state DOTs to assess and advance transportation-related GHG reduction strategies in planning and programming. The guidance will support state DOTs’ efforts to integrate GHG emissions considerations into their decision-making processes as well as methods appropriate for collaborative activities undertaken with partners to shape outcomes outside the purview of a state DOT. The guidance should be relevant for the evolving role of state DOTs and be adaptable to a changing regulatory environment at the state and federal levels, while also considering uncertainties related to future travel behavior, the future vehicle fleet, and other demographic and technological changes.
The project will also broaden the practice of addressing GHG emissions in state DOT decision making through targeted implementation activities to support state DOT adoption or updating of GHG emissions reduction methods.
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