Per passenger mile, light rail and other commuter transportation modes are less energy intense than light-duty passenger vehicles. However, bus transit and light-duty trucks are more energy intense. For freight transport, heavy-duty trucks are considerably more energy intense than rail on a ton-mile basis.
Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Transportation Energy Data Book: Edition 24-2004. Table 2.12, Energy Intensities of Highway Passenger Modes, 1970-2002, Table 2.13; Energy Intensities of Non highway Passenger Modes, 1970-2002, and Table 2.15, Energy Intensities of Freight Modes, 1970-2002. December 2004. Web site: http://cta.ornl.gov/data/chapter2.shtml 28 June 2005.
Highway vehicles are the largest users of transportation energy, accounting for 81 percent of the total.
Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy. Transportation Energy Data Book: Edition 24-2004, Table 2.5, Transportation Energy Use by Mode, 2001Ð2002. December 2004. Web site: http://cta.ornl.gov/data/chapter2.shtml (table 2.5) 28 June 2005.
Greenhouse gases trap heat within the earth's atmosphere. Although most greenhouse gas occurs naturally and helps to keep the earth hospitable to life, it also is generated by human activities. Carbon dioxide (CO2) emissions account for more than 80 percent of the U.S. greenhouse gas emissions. These emissions are contributing to changes in the planet's temperatures that could lead to harmful effects, such as sea-level rise and changes in global hydrological patterns. Although the United States makes up 4.7 percent of the world's population, it emits about one-fifth of carbon emissions from fossil fuel combustion (5,736 million metric tons of CO2 in 2002).
In contrast to most criteria pollutants, emissions of greenhouse gases have been rising from all sectors. From 1990 to 2002, carbon emissions from transportation grew by almost 18 percent. Overall, transportation contributes approximately one-third of national carbon emissions.
Source: Bureau of Transportation Statistics. National Transportation Statistics 2003. Table 4-49.
March 2004. Web site: http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/national_transportation_statistics/2003/html/table_04_49.html
28 February 2005. U.S. Department of Energy, Energy Information Office. June 30, 2004. Web site:
http://www.eia.gov/neic/press/press238.html, 28 February 2005.
The United Nations Department of Economic and Social Affairs. World Population Prospects: The 2004 Revision - Population Database. Web site: http://esa.un.org/unpp/ 28 February 2005.