GAO Report Analyzes How to Measure Transpo GHG Emissions

The Obama Administration issued a rule requiring states and metropolitan planning organizations (MPOs) to measure the greenhouse gas (GHG) emissions of transportation projects. The Trump Administration repealed the rule before it could become effective. Then the Biden Administration reissued a similar rule last October.

A new report from the U.S. Government Accountability Office examines exactly how states and MPOs would go about measuring those emissions.

The report, entitled Climate Change:State and Local Efforts to Reduce Greenhouse Gas Emissions from Vehicles, was commissioned by the House and Senate Appropriations Committees, who, in the conference report to accompany the fiscal 2022 DOT appropriations act, ordered GAO to “assess and provide a report no later than 270 days after enactment of this act on: (1) the extent to which Federal agencies, states, and MPOs are currently collecting performance information on transportation-re- lated GHG emissions; (2) how the information on GHG emissions is used to inform transportation investment decisions; and (3) opportunities for the FHWA to better leverage this information.”

The GAO report is based on interviews with, and analysis of, a sampling of 10 state DOTs and 10 MPOs, as well as interviews with four federal agencies and a few stakeholder groups (listed in Appendix I here), as well as a questionnaire sent to all 50 state DOTs and returned by 39 of them. The study builds on an earlier Transportation Research Board report.

As far as who is measuring or estimating already, “About 40 percent of the states that responded (16 of 39) to the question reported that they had developed greenhouse gas inventories for the transportation sector or worked with a partner agency to develop one. A little over half of the states that responded (23 of 39) indicated that they had not developed a greenhouse gas inventory or forecast for the transportation sector.”

Methodologies. Among the entities that do try to measure GHG emissions, there were differing methodologies for estimation:

  • Fuel data – “We found examples of state DOTs using fuel data to estimate on-road greenhouse gas emissions—which are also data that FHWA included in its proposed rule—either alone or in conjunction with other data. For example, Vermont DOT officials told us that fuel data are currently the basis of their estimates. California state officials said that they have 28 sources of data that contribute to their tracking of on-road greenhouse gas emissions, including fuel and travel demand data.”
  • VMT data – “the state DOTs and MPOs we interviewed more commonly used VMT data when estimating greenhouse gas emissions. In comments submitted to FHWA on the proposed rule, some state DOTs and stakeholders stated that using VMT data had advantages over using fuel data. For example, although they supported FHWA’s proposed rule, 11 state DOTs [California, Colorado, Connecticut, the District of Columbia, Hawaii, Illinois, Minnesota, Oregon, Pennsylvania, Vermont, and Washington] noted that VMT data may be better aligned with existing state programs and practices than fuel data. Similarly, the Association of Metropolitan Planning Organizations commented that using VMT data would provide consistency between regions and states. According to these comments, VMT data would help states and MPOs identify whether any emissions reductions were due to VMT-reducing strategies or technological changes. We also found examples of state DOTs and MPOs using a combination of VMT data and other data. For example, officials from an MPO in Vermont told us that they use a combination of vehicle mix, speed, roadway, and other data along with VMT data when estimating emissions.”
  • Modeling – “Our review also found examples of the modeled data that selected state DOTs and MPOs used to estimate on-road greenhouse gas emissions. These entities most commonly used EPA’s Motor Vehicle Emission Simulator (MOVES). MOVES is an emissions modeling system that estimates emissions for mobile sources at the national, county, and project level for greenhouse gas and other air pollutants. California is a notable exception to using MOVES, because the state has developed its own model. According to state officials, this model can estimate emissions rates of air pollutants, including greenhouse gas emissions, for on-road vehicles that are operating in California across a range of past and future years.”

Non-participation. As far as the states that don’t currently measure or estimate GHG emissions: “The selected state DOTs that do not currently estimate on-road greenhouse gas emissions cited a number of reasons, such as the type of traffic in their state, status of state planning efforts, and state priorities. Montana DOT officials told us they do not track or estimate on-road greenhouse gas emissions because the majority of the roads under their jurisdiction are rural roads that are not on the National Highway System, and do not have congestion issues. According to Michigan DOT officials, the state only recently developed a climate plan in 2022, and they are early in the process of identifying implementation strategies to align with the plan, including how they will estimate on-road greenhouse gas emissions. Arkansas DOT officials stated they would not estimate on-road greenhouse gas emissions as standard practice unless specifically required to do so by a federal or state regulation.”

Specific difficulties for MPOs. AMPO told GAO that “two-thirds of all MPOs are small, with potentially one or two staff members. As a result, they often do not have the subject matter expertise or staff resources of medium- and large-sized MPOs to analyze greenhouse gas emissions.” In addition, data that is available on a statewide basis is not always broken down at a sub-state level: “For example, officials from an MPO in Vermont told us that data on certain fuel (oil, propane, and gasoline) at the municipal level are not readily available, creating challenges for them in making estimates. Officials from an MPO in Georgia told us that private sector movement data are too expensive for most MPOs to purchase.”

Not many entities currently use GHG reduction targets. The study reports that “Specifically, six of 40 responding state DOTs reported having a policy as of 2018 that sets system-wide goals or targets for reducing transportation greenhouse gas emissions, according to a survey in NCHRP’s 2022 report.37 (The survey did not ask whether states had targets specific to on-road emissions.) Additionally, 16 of 39 responding state DOTs reported having some sort of goals, objectives, or performance measures related to greenhouse gas emissions in their long-range transportation plans, but only three of those states reported having quantitative performance measures and reduction targets.”

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