Greenhouse Gas Emissions

Greenhouse Gas Emissions

The transportation sector’s greenhouse gas (GHG) emissions in 2002 totaled 1,861.4 teragrams of carbon dioxide equivalent (TgCO2Eq), 27 percent of total U.S. GHG emissions.1 Transportation emissions have grown 22 percent since 1992, while total U.S. emissions rose 14 percent [1].

Carbon dioxide (CO2) accounted for 83 percent of U.S. GHG emissions in 2002 [1]. Nearly all (97 percent) of these emissions are generated by the combustion of fossil fuels; transportation was responsible for 1,767.5 TgCO2Eq (31 percent) of CO2 emissions. Transportation CO2 emissions grew 21 percent between 1992 and 2002, an average annual change of 1.9 percent (figure 10-4). Heavy-truck emissions grew the most over the period (46 percent). Aircraft emissions rose more slowly, increasing 16 percent from 1992 to 2000, then declining 8 percent in the following two years, most likely a “9/11 effect” that reduced 1992 to 2002 growth to 6 percent.2 (See box 10-B for information on the two sources of U.S. GHG data.)

Highway vehicles emitted 79 percent of all transportation CO2 emissions in 2002 and rose at an average annual rate of 2.2 percent between 1992 and 2002. Passenger cars and light-duty vehicles, which include pickup trucks, sport utility vehicles, and vans, were responsible for 79 percent of highway emissions (figure 10-5).

Most air pollutants impact local or regional air quality. Greenhouse gases, however, have the potential to alter the earth’s climate on a regional and global scale.


1. U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2002, available at, as of May 2004.

1 A teragram is a trillion grams.

2 The GHG data here cover domestic emissions only. Figure and table 10-4 include data on international bunker fuel emissions, which result from the combustion of fuel purchased domestically but used for international aviation and maritime transportation.