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Questions and Answers

(Updated January 2016)

What are the primary greenhouse gas (GHG) emissions from transportation?

The primary GHGs produced by the transportation sector are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and hydrofluorocarbons (HFC). Carbon dioxide, a product of fossil fuel combustion, accounts for 95 percent of transportation GHG emissions in the U.S.

Transportation GHG emissions account for 29 percent of total U.S. GHG emissions and almost 4 percent of global GHG emissions. These estimates account only for tailpipe emissions from burning fossil fuels to power vehicles and do not account for GHGs emitted through other transportation lifecycle processes, such as the manufacture of vehicles, the extraction and refining of fuels, and the construction and maintenance of transportation infrastructure. Including these processes, U.S. transportation lifecycle greenhouse gases are estimated to account for roughly 5 percent of global GHG emissions.

Are there ambient air quality standards for GHG emissions?

No, there are not ambient air quality standards for GHG emissions. Unlike air pollutants with national ambient air quality standards (NAAQS), the primary GHG emissions are well mixed in the atmosphere and do not create toxic hot spots. Rather than causing a local air quality problem, GHG emissions cause impacts by trapping heat in the atmosphere, leading to increased temperatures, sea level rise, and changes in precipitation patterns.

At what level would a transportation GHG analysis be appropriate?

Transportation system planning carries a large potential for GHG reduction, as this is where communities make decisions on future transportation investments. Those decisions, in addition to local level land use decisions, will influence travel patterns and emissions from vehicles on the system for many decades.

Transportation law requires States and metropolitan planning organizations (MPOs) to consider multiple planning factors, including “environment and energy,” as part of the transportation planning process. Burning of fossil fuels such as petroleum for energy produces GHG emissions that cause negative impacts on the environment. As such, GHG emissions analysis would be appropriate under the environment and energy planning factor.

A planning level GHG analysis may be incorporated into the National Environmental Policy Act (NEPA) environmental review process for projects included in the plan. A planning level analysis is helpful given its system-wide approach, and its broader geographic scope and longer time scale. However, a state may also choose to perform a project or corridor analysis because of state laws and regulations. There are examples of both planning and project level analyses included in this document. Addressing both climate change mitigation and adaptation issues upfront in the planning process may help to facilitate decision-making and improve efficiency at the program level, and it may also inform the analysis and stewardship needs of project-level decision-making. Current law encourages the integration of information and products developed in highway and transit planning into the NEPA review process – see the Environment and Planning Linkage Processes Legal Guidance.

Transportation legislation requires State DOTs and MPOs to consult with State and local resource agencies when developing long-range statewide or metropolitan transportation plans and to include a discussion of potential mitigation activities and potential areas to carry out these activities. Including climate change mitigation and adaptation discussions in the consultation process for statewide and metropolitan transportation plans will improve planning and project-level decision-making, can provide information for use in the NEPA process, and can help foster cooperation among transportation, resource and land use agencies. FHWA and FTA issued a joint memo (FHWA/FTA Planning Program Funds to Support Integration of Transportation, Land Use, and Climate Change dated November 17, 2008) to clarify that metropolitan and statewide planning funds are eligible to be used to address the integration of transportation, land use, and climate change, provided that all federally-mandated planning activity is being accomplished.

How could State DOTs and MPOs integrate climate change considerations into their transportation planning processes?

Transportation planners have many factors to consider when developing plans (e.g., sustainability, environmental justice, safety, state-of-good-repair, land use, the economy, etc.). Climate change consideration is a relatively new entry into this list of issues. A comprehensive transportation plan is one that has a holistic approach and considers all factors as relevant, dynamic and interactive; planners should not treat climate change (or any factor) as a completely separate and overriding component of the Plan. A cooperative and balanced approach is best. In addition, it is appropriate to acknowledge that the public audience to which the Plan is directed may not hold climate change considerations on the top of its priority list. One successful approach is to emphasize that the Plan's benefits of energy conservation and efficiency (e.g., national security, economic benefits, stewardship of the planet) comes with the co-benefit of GHG reduction.

Discussion of climate change is becoming more common in transportation planning documents. Many state DOTs and MPOs are recognizing the role that transportation policies and investments play in contributing to the emissions of GHGs and conversely, the potential impact of climate change on transportation systems. Some long-range transportation plans (LRTPs) in particular are highlighting climate change among a new generation of environmental and sustainability issues that shape transportation planning objectives.

In an effort to assist states and MPOs in this effort, FHWA funded a study in 2008 entitled Integrating Climate Change into the Transportation Planning Process. The study examined how a number of MPO's are approaching the subject and identified opportunities for practitioners to address climate change within several key elements of transportation plans. Each of these elements can incorporate climate change directly, by explicitly addressing climate change, and indirectly, by addressing elements of transportation that are linked to climate change. Components within both statewide and metropolitan transportation plans that can include climate change are:

In addition, the Strategic Highway Research Program 2 (SHRP 2) completed a study entitled Incorporating Greenhouse Gas Emissions into the Collaborative Decision-Making Process (SHRP 2-C09). The report presents information to practitioners on how GHG emissions can be incorporated into transportation planning and decision making. The report is accompanied by a Practitioners' Handbook that provides a useful reference guide on how GHG emissions and energy factors can be considered in different planning and decision-making contexts. The Denver Regional Council of Governments (DRCOG), Massachusetts DOT and Washington DOT are implementing this SHRP2 product.

What model should transportation agencies use to calculate GHG emissions?

The EPA's MOVES model is the recommended model for calculating on-road GHG emissions. The MOVES model develops on-road energy consumption and emissions estimates based on speed and vehicle power output. MOVES has already been used by several State and local agencies for GHG analyses. California's EMFAC model also estimates CO2 emissions; however, since EMFAC reflects the California fleet and emissions control programs, it is only suitable only for use in California.

What FHWA tools and resources are currently available to analyze transportation GHG emissions and reduction strategies?

Transportation practitioners are often asked to respond to questions from the public and decision makers about the implications transportation plans and projects have on GHG emissions. FHWA tools and resources to assist include:

What State requirements are there on GHG analyses for transportation plans, programs, and projects?

Several States have specific requirements regarding GHG emissions analysis for transportation plans, programs, and projects. Following are some examples; but this should not be considered a comprehensive list:

New York. The State's Energy Plan requires an energy and GHG analysis for MPO transportation plans and TIPs and for all regionally significant projects and other projects that may lead to large increases in vehicle miles traveled. The environmental documents for those proposed projects typically include an analysis of projected CO2 emissions associated with construction and operation of each alternative.

Massachusetts. Certain projects subject to the Massachusetts Environmental Policy Act are required to include a quantification of GHG emissions as well as consideration of measures to avoid, minimize or mitigate such emissions. Massachusetts also has GHG planning level requirements under its GreenDOT initiative (

Washington. The WSDOT Environmental Procedures Manual states that climate change, including effects of projects on GHG emissions, should be discussed in EAs and EISs.

California. California SB 375 requires the State's MPOs to include "sustainable communities" strategies in their regional transportation plans for the purpose of reducing GHGs.

Oregon. HB 2186 (PDF) requires creation of a Metropolitan Planning Organization (MPO) Greenhouse Gas Emissions Task Force to evaluate alternative land use and transportation scenarios that would meet community growth needs, while reducing greenhouse gas emissions and recommend future legislative action to support such efforts. HB 2186 Section 10 applies to all six of Oregon's Metropolitan Planning Organizations which include: Portland Metro MPO, Salem Keizer Area Transportation Study MPO, Corvallis Area MPO, Central Lane MPO, Rogue Valley MPO, and Bend MPO. (per ODOT website

Does FHWA have examples of GHG analyses for transportation plans, projects and programs for States and/or MPOs?

NEPA Documentation Examples:

New York. New York State DOT includes a quantitative CO2 emissions analysis in environmental documentation to meet State requirements. Many examples are included on NYSDOT's website.

Washington. To satisfy State requirements, the Alaska Way Viaduct and SR 520 FEISs include GHG and climate change discussions in the energy, air quality, and cumulative effects sections.

Center for Climate Change Law at Columbia Law School. The Center for Climate Change at Columbia Law School published a database that covers how various Federal agencies address climate change issues in EIS documents.

Transportation Planning Examples:

California – Senate Bill 375 (2008) in conjunction with AB 32 requires mandatory GHG targets to be set and Sustainable Communities Strategies (SCS) to be developed through MPOs Regional Transportation Plans under an integrated land use and transportation planning framework. CA employed a "bottom-up" approach to estimate the anticipated changes and differences among regions, using data and analysis developed by the regions. The Regional Targets Advisory Committee (RTAC) provided a final report to the CA Air Resources Board in September 2009 outlining the targets. Due to the uniqueness of each MPO and region, proposed targets were looked at in the following groups: four largest MPOs, eight MPOs in the San Joaquin Valley, and six remaining MPOs. The targets for the State's four largest MPO's were 7 to 8 percent by 2020, and between 13 and 16 percent in 2035 through regional land use and non-technology based transportation strategies. For the San Joaquin Valley region CARB proposed per capita GHG reductions of 5 percent by 2020 and 10 percent by 2035. The remaining six MPOs, CARB's proposed targets reflected current projections in their most recently adopted regional plans.

The RTAC process for setting GHG reduction targets under SB 375 was a collaborative effort among the state's MPOs and CARB, with support from Caltrans and the California Transportation Commission regarding modeling and regional transportation plan guidance. The RTAC recommended a seven-step process for the target setting analysis with the final step being the adoption of targets by CARB in September 2010.

The RTAC recommended that targets be expressed as a percent reduction in per capita GHG emissions from a 2005 base year. These metrics were chosen because they take into account population growth, and 2005 was the most recent year that could be used uniformly for all MPOs. As such, the MPOs prepared an analysis of their adopted fiscally constrained RTP, including estimates of per capita GHG emissions for the 2005 base year and for years 2020 and 2035. MPO and CARB staffs worked together to ensure consistency in analysis, including use of certain long-range planning assumptions.

In preparing alternative scenarios, MPOs considered a variety of GHG reduction strategies related to transportation demand management (TDM), transportation systems management (TSM), transportation system improvements, land use measures and pricing measures. These include the use of pricing options, such as freeway toll express lanes, dynamic parking pricing, and various fuel taxes or fees. A list of measures, alternative scenarios, and data outputs related to performance indicators were identified for each MPO. Performance indicators included GHG emission levels at target years, transportation performance measures, economic performance measures, social equity performance measures, housing production performance measures, and other environmental performance measures.

Details and examples of the various analyses and methodologies used by the CA MPOs to meet the GHG targets established by CARB can be found at:

Washington – In 2008, House Bill 2815 established GHG emissions and VMT reductions – including goals for GHG emissions reduction to 1990 levels by 2020; 25 percent below 1990 levels by 2035; and 50 percent below 1990 levels by year 2050. The Bill also called for an 18 percent VMT per capita reduction below business-as-usual projections for 2050; 30 percent by 2035; and 50 percent by 2050. In 2009, the Governor issued Executive Order (EO) 09-05 which directed the Washington State Department of Transportation (WSDOT) to work with the four largest Regional Transportation Planning Organizations and MPOs to "develop and adopt regional transportation plans that will, when implemented….reduce GHGs and achieve statutory benchmarks to reduce annual per capita VMT." In 2010 WSDOT issued a Sustainable Transportation Report, which provides findings and recommendations on the EO as well as intended approaches and methodologies for GHG analysis.

Oregon - In 2009 and 2010 the Oregon Legislature passed SB 1059, requiring the Oregon Department of Transportation (ODOT), the Department of Land Conservation and Development (DLCD), and other state agencies to work together and examine ways to reduce GHG emissions from passenger vehicles. The legislation required the development of a statewide transportation strategy (STS) and its adoption by Oregon Transportation Commission (OTC), scenario planning guidelines, and implementation toolkit, GHG targets, and a public education program.

In response to the legislative requirements, the Oregon Department of Transportation (ODOT) developed the GreenSTEP (Greenhouse gas State Transportation Emission Planning) model to provide modeling support for the development of a statewide strategy for reducing transportation sector GHG emissions. The decision was made to develop GreenSTEP after it became apparent that existing models would not be able to address the wide variety of policy actions that would make up a statewide GHG strategy.

The model is being used to estimate VMT and GHG emissions both statewide and within the various metropolitan areas in Oregon, and combines household level modeling of vehicle types and usage with more aggregate level modeling of factors such as fuel types. The model is being used to assist in the development of a statewide strategy for reducing greenhouse gas emissions from the transportation sector in Oregon.

Oregon is just beginning the process of setting targets and preparing plans: The Agencies Technical Reportfound that the six MPOs proposed reduction goals varied between 40 percent reduction from 1990 to 2 percent reduction from 1990 by 2035. More information on OR's GHG analysis and the use of the GreenSTEP Model can be found at the Oregon Sustainable Transportation Initiative (OSTI) website at:

San Diego Association of Governments (SANDAG). SANDAG considers climate change in the trends, challenges, goals, and strategies of its transportation plan. In compliance with the California Environmental Quality Act, SANDAG prepared an Environmental Impact Report (EIR) (60 MB) for its 2030 Regional Transportation Plan. In the EIR, SANDAG analyzes the plan's climate change impacts, identifies them as "significant and unavoidable," and establishes mitigation measures to address them. A few examples of mitigation measures SANDAG included are increasing the number of vanpools, analyzing pricing strategies for reduced transit fares and tolling, and examining a variety of electric transportation initiatives. The EIR also quantifies the GHG emissions resulting from the plan.

Sacramento Area Council of Governments (SACOG). SACOG incorporates climate change mitigation in the trends and challenges and policies of its Metropolitan Transportation Plan (MTP). The EIR for the MTP analyzes the plan's global warming impacts and proposes mitigation measures. Examples of mitigation strategies SACOG included are adopting a transportation pricing policy, creating an alternative fuel vehicle and infrastructure toolkit for local governments, and creating a public education program on individual transportation behavior and climate change. The SACOG also released a Preferred Blueprint Scenario as part of the MTP. The document depicts a way for the region to grow through the year 2050 promoting climate-friendly strategies such as compact, mixed-use development and more transit choices. The Preferred Blueprint Scenario serves a guide to local governments for growth and transportation planning.

Metropolitan Transportation Commission (MTC). Some MPOs, such as the San Francisco MPO, are experimenting with the use of GHG emissions as a measure for evaluating projects or packages of projects in the decision-making process. MTC used GHG emissions as a performance measure to rank and evaluate some projects in the development of its most recent LRTP. Packages of projects were also evaluated using the GHG emissions criterion. The use of these criteria will have a second-order effect on those projects selected for TIPs. MTC set a performance goal of achieving a 40 percent reduction in GHG emissions by 2035; they found that, even using the most aggressive packages of transit, land use, and pricing strategies, their plan alternatives fell short by about half.. MTC also evaluated the cost-effectiveness of the strategy packages --see for more information on the MTC analysis.

Updated: 2/17/2016
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