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Handbook for Estimating Transportation Greenhouse Gases for Integration into the Planning Process

Chapter 1 - Introduction

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1.1 - Background and Purpose

Transportation sources are a significant contributor to greenhouse gas (GHG) emissions nationally and are often considered a key component of climate change mitigation efforts. State departments of transportation (DOTs) and metropolitan planning organizations (MPOs), together with transit agencies, local governments, and other partners, have the responsibility for transportation planning, which along with federal and state policies can affect GHG emissions patterns. Transportation planning requires comprehensive consideration of possible strategies and diverse viewpoints gathered, in part, through stakeholder and public engagement. It includes assessing a range of policy, investment, and system management and operations strategies, and their effects.

Recognizing that the transportation planning process plays a fundamental role in the state's, region's, or community's vision for its future, some states and metropolitan areas are incorporating GHG reduction goals into their planning efforts. While there is no Federal requirement for consideration of GHG impacts in statewide and metropolitan transportation planning, some agencies are moving ahead with efforts to quantify GHGs and explore transportation strategies to reduce these emissions.

For instance, in response to statewide climate change requirements or energy policy initiatives, MPOs in New York, California, and Washington have been incorporating GHG analyses into their metropolitan transportation plans, and MPOs in Oregon are in the process of incorporating GHG analyses into their regional planning processes. Even in states without any GHG requirements, some State DOTs and MPOs are beginning to analyze GHG emissions, including both past and current emissions as well as future forecasts, to help inform on-going climate change mitigation efforts and to make more informed transportation investment decisions. Many states also have produced GHG inventories and have identified potential transportation mitigation strategies through the development of climate action plans. These inventories and climate change action plans may be a foundation for states and regions to explore transportation policies and strategies in more detail through the statewide or metropolitan transportation planning process. 1

This Handbook and other resources have been developed that provide information about GHG analysis tools. For example, the National Cooperative Highway Research Program (NCHRP) report Assessment of Greenhouse Gas Analysis Techniques for Transportation Projects2 identifies 17 tools or methods that can be used to analyze the GHG implications of transportation projects. The report Greenhouse Gas Analysis Tools3 prepared for the Washington State Department of Commerce introduces a methodology to identify tools that can be used to estimate GHG emissions, and includes a description of available tools. Also, GHG emissions analysis may use the same tools and data as the emissions analysis for criteria pollutants that many MPOs currently conduct for Clean Air Act (CAA) transportation conformity.

Many State DOTs and MPOs are just beginning to explore how to analyze GHG emissions in relation to their transportation plans. They may have questions such as:

This Handbook is intended to help State DOTs and MPOs of all sizes and capabilities understand possible approaches, data sources, and step-by-step procedures for analyzing GHG emissions for use in the transportation planning process. It is intended for use by individuals who are involved in deciding how their organization will perform a GHG analysis at a statewide or metropolitan level. This could include planning directors or other staff who would like to better understand available options for quantifying GHGs that can be implemented in their existing process. The Handbook is intended to be user friendly and informative, particularly for State DOTs and MPOs that have limited experience with emissions analysis. It provides an overview of the analytical process required and directs users to more detailed user manuals and technical resources regarding specific models and tools.

Handbook Supports Planning Level Analysis

Keep in mind that the methods described in this Handbook are designed for use at the statewide or regional levels. Some methods may also be applicable at a smaller area-wide level, such as a county or municipal level. Throughout this Handbook, the term "local" level is intended to mean the county or municipal level, not the project level.

The Handbook addresses GHG emissions analysis within the context of statewide and metropolitan transportation planning, not at the individual project level. Although the intended audience is State DOTs and MPOs, some of the methodologies included in the Handbook can be appropriately applied to the local, meaning the county or municipal level. Many counties and cities are developing GHG inventories or conducting analyses of GHG reduction strategies, and some local governments are partnering with their respective states and MPOs. In addition, some areas may be interested in transportation goals related to reducing fuel use or energy consumption. While this Handbook focuses on GHG emissions, many of the techniques and resources presented here apply equally to either analyzing GHG emissions or fuel use/energy consumption.

1.2 - Development of this Handbook

This Handbook was developed with input from State DOT and MPO practitioners from across the country, including a Greenhouse Gas Assessment in Transportation Team (GGATT) convened specifically to help shape this document. Developing the Handbook involved the following key steps:

Based on the documented information, and input from the GGATT and other transportation practitioners, the information was then organized in the form of this Handbook to provide a practical resource for State DOT and MPO staff.

1.3 - Handbook Organization

This Handbook describes GHG analysis approaches and lays out steps associated with each of these methods, along with information on data sources, examples of their application, and resources for further information.

The Handbook is organized as follows:

Section 2: Overview: Estimating GHG Emissions in the Planning Process provides an introduction to GHG emissions, why an agency might be interested in analyzing GHG emissions, and the types of analyses that may be conducted in the context of statewide and metropolitan transportation planning. It also provides an overview of primary GHG estimation methods. This section may be particularly helpful for staff who have limited experience with emissions analysis and those who want a broad overview of different approaches.

Section 3: What Methodologies are Applicable for your Situation is designed to help the Handbook user identify an appropriate method or methods, based on the specific needs and situation of the agency.

Sections 4 through 8 focus on methodologies for estimating GHG emissions. For each methodology, the key steps and data options are reviewed, along with strengths and weaknesses of each approach and examples of agencies that have followed the approach. A summary table is included at the beginning of each section to help the user understand the basic requirements of the approach. These sections also provide references to additional resources, as well as tips to keep in mind in regard to these approaches.

Section 4: Fuel-based Methods describes methods that rely on fuel consumption data, including both inventory and forecasting methods.

Section 5: Vehicle Miles Traveled (VMT)-based Methods describes approaches that rely on vehicle travel data and connect this information to an estimate of emissions using emission factors or an emissions model. This section discusses methods relying on a range of data to estimate VMT and travel activity, including vehicle, household, and land use data, as well as data from the Highway Performance Monitoring System (HPMS), and network-based travel models. It also discusses various approaches to estimating emissions, including use of the U.S. Environmental Protection Agency's (EPA) Motor Vehicle Emissions Simulator (MOVES) model, the preferred tool for developing emissions estimates.

Section 6: Alternative GHG Estimation Approaches describes two other types of approaches that do not rely directly on fuel consumption or VMT data: 1) commodity-flow based methods to estimate freight truck emissions and 2) use of the FHWA's Energy and Emissions Reduction Policy Analysis Tool (EERPAT) to analyze scenarios that include a range of policy and transportation system changes.

Section 7: Specific Transportation Strategy Analysis Methods identifies additional tools and approaches that can be used to analyze specific types of transportation strategies, such as transportation demand management (TDM), land use, transportation system management (TSM), eco-driving, and freight strategies. These strategies are often not well accounted for in GHG forecasts and require separate analysis.

Section 8: Additional Considerations: Lifecycle Analysis and GHG Emissions from Transportation Construction and Maintenance reviews 1) lifecycle emissions analysis (LCA), a type of analysis that aims to improve the understanding of GHG emissions from transportation and upstream sources, such as fuel processing and distribution; and 2) analysis of emissions from transportation infrastructure construction and maintenance.

Section 9: References provides links to more detailed documentation of models, and information on additional resource documents.

1 Transportation components of state climate action plans are often quite limited, and forecasts and strategy analyses may require updates. See: FHWA, "Review and Assessment of State Climate Action Plans," prepared by ICF International, 2009, Also, NCHRP Report 20-24, Task 59, "Strategies for Reducing the Impacts of Surface Transportation on Global Climate Change: A Synthesis of Policy Research and State and Local Mitigation Studies," prepared by Parson Brinckerhoff, 2009,

2 NCHRP Project 25-25 Task 17, "Assessment of Greenhouse Gas Analysis Techniques for Transportation Projects," prepared by ICF International, 2006.

3 Washington State Department of Commerce, "Greenhouse Gas Analysis Tools," prepared by Fehr & Peers, 2009,

Updated: 03/27/2014
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