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Greenhouse Gas Emissions from the U.S. Transportation Section: 1990-2003
Report published March 2006
The full report is available at http://www.epa.gov/otaq/climate/420r06003.pdf (68 pages, 1.14MB, About PDF Files).
Although transportation is a vital part of the economy and is essential for everyday activities, it is also a significant source of greenhouse gas (GHG) emissions. In 2003, the transportation sector accounted for about 27 percent of total U.S. GHG emissions, up from 24.8 percent in 1990. Transportation GHG emissions increased by a larger amount than any other economic sector(1) over this period, growing from 1509.3 teragram (Tg) CO2 Eq. in 1990 to 1,866.7 Tg CO2 Eq. in 2003, an increase of 24 percent(2). GHGs from all other sectors increased by a total of 9.5 percent over the same timeframe. Looking forward, transportation GHGs are forecast to continue increasing rapidly, reflecting the anticipated impact of factors such as economic growth, increased movement of freight by trucks and aircraft, and continued growth in personal travel. According to the U.S. Department of Energy (DOE), transportation energy use is expected to increase 48 percent between 2003 and 2025, despite modest improvements in the efficiency of vehicle engines. This projected rise in energy consumption closely mirrors the expected growth in transportation GHG emissions(3). [a teragram is equal to 1 million metric tons]
This report was developed by the U.S. Environmental Protection Agency’s (EPA) Office of Transportation and Air Quality (OTAQ) to help transportation agencies, the transportation industry, researchers, and the public better understand the connection between transportation and GHG emissions in the United States. The GHG emissions estimates presented in this report are taken from the official GHG Inventory produced by EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2003 (“U.S. GHG Inventory”). As a complement to the U.S. GHG Inventory, this report includes additional detail on GHG emissions from transportation and non-transportation mobile sources. It also analyzes factors affecting emissions, uncertainty in the data, and emerging issues.
The report is organized in the following sections:
- Overview of Greenhouse Gas Emissions and Transportation, provides a brief introduction to specific GHGs and their measurement. It also compares the nation’s transportation emissions to other sectors, and discusses variables contributing to the rise transportation GHGs.
- Light-Duty Vehicles, describes GHG emissions from light-duty motor vehicles, currently the largest sources of transportation GHGs.
- Heavy-Duty Vehicles, addresses emissions and trends for heavy-duty vehicles.
- Aircraft Section discusses emissions from aircraft, which are the largest source of non-road transportation GHG emissions.
- Other Non-Road Transportation, characterizes emissions from boats and ships, rail, and pipelines.
- HFCs from Mobile Air Conditioners and Refrigerated Transport, describes HFC emissions from transportation sources, which include mobile air conditioners and refrigerated transportation units.
- Non-Transportation Mobile Sources, discusses GHG emissions from non-transportation mobile sources, such as agricultural equipment, construction equipment, and other utility equipment.
- Estimating Transportation GHG Emissions—Methodology and Uncertainty Section briefly describes methods that are used to estimate transportation GHG emissions and explores uncertainties in the calculations.
- Lifecycle Transportation Emissions, examines GHG emissions from a broader lifecycle perspective, including activities such as fuel processing and distribution, vehicle manufacture and vehicle maintenance.
- GHG Emissions Projections and Emerging Issues Section provides forecasts of GHG emissions from transportation sources through 2025 and highlights some of the issues affecting trends in GHG emissions from transportation during this time period.
(1) The “economic sectors” referred to in this report do not represent official Intergovernmental Panel on Climate Change (IPCC) categories. EPA has found it useful to estimate emissions by sectoral categories that are commonly used for policy analysis. One method allocates emissions to seven different “economic sectors,” which include Electricity Generation, and the non-electricity component of all six other sectors (Transportation, Industry, Agriculture, Commercial, Residential and U.S. Territories). The second method distributes the emissions from Electricity Generation to the remaining “end use” sectors.For purposes of simplicity, this report uses the second categorization when referring to sectoral estimates.
(2) U.S. Environmental Protection Agency, 2005. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2003. Washington, DC. The total transportation sector GHGs cited in this report are slightly lower than the transportation sector totals reported in the published Inventory (approximately 0.7 to 0.9 Tg lower from 1990 to 2003). This small increment represents “other” non-transportation mobile sources, such as lawn mowers and leaf blowers, which are counted as transportation in the published Inventory but not this report. GHG emissions are typically reported in terms of CO2 equivalent (CO2 Eq.) in order to provide a common unit of measure, and because CO2 is the most prevalent of all GHGs.
(3) U.S. Energy Information Administration, Annual Energy Outlook 2005 with Projections to 2025, Table A2. U.S. Department of Energy, Energy Information Administration, Washington, DC.