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.
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 (https://www.trb.org/Main/Blurbs/166936.aspx). The 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.