Greenhouse Gas Emissions

Greenhouse Gas Emissions

The transportation sector's greenhouse gas (GHG) emissions totaled 1,864 teragrams of carbon dioxide equivalent (TgCO2Eq) in 2003.1 This represented 27 percent of total U.S. GHG emissions in 2003 (box 15-B). Transportation emissions grew 20 percent since 1993, while total U.S. emissions rose 10 percent2 [1].

Carbon dioxide (CO2) accounted for 85 percent of U.S. GHG emissions in 2003. Nearly all (95 percent) of these emissions are generated by the combustion of fossil fuels, with transportation responsible for 1,781 TgCO2Eq (30 percent) of CO2 emissions [1]. Transportation CO2 emissions grew 19 percent between 1993 and 2003 (figure 15-3). Heavy-duty truck emissions grew the most over the period (51 percent), while aircraft emissions rose the least (1.9 percent). Aircraft emissions did rise 15 percent between 1993 and 2000 but then declined 11 percent from 2000 through 2003, most likely because of the September 11, 2001, terrorist attacks and the ongoing economic downturn that suppressed air travel growth in 2001 and 2002.

Highway vehicles emitted 82 percent of all transportation CO2 emissions in 2003, rising 23 percent between 1993 and 2003. Passenger cars and light-duty vehicles, which include pickup trucks, sport utility vehicles, and vans, generated 76 percent of highway CO2 emissions (figure 15-4).

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: 1990-2003, tables 2-14 and ES2, available at, as of April 2005.

1 A teragram is a trillion grams.

2 The GHG data here cover domestic emissions only. Figure and table 15-4 include data on international bunker fuel emissions, which result from the combustion of fuel purchased domestically but used for international aviation and maritime transportation.