Only when a sizable fraction of in-use vehicles incorporates efficiency improvements and new power trains can the effect of these changes on the nation’s energy use and greenhouse gas emissions reach significant levels. The panel constructed some illustrative scenarios of vehicle and technology deployment as a means of estimating the potential overall effects of improved passenger vehicles and technologies on fuel consumption and the environment. The results are discussed in Section 3.3.

Finally, Section 3.7 outlines the challenges that will have to be met and the impediments that will have to be overcome to improve energy efficiency in transportation, and Section 3.8 presents the panel’s findings for the sector.

Energy use for transportation in the United States has experienced tremendous growth over the past several decades, although the trend registered brief pauses during the economic recessions of 1974, 1979–1982, 1990–1991, and 2001.

In 2007 the United States consumed 29 quads (quadrillion British thermal units, or Btu) of energy for transportation, or about 28 percent of total U.S. energy use. Moreover, the sector used more than 70 percent of the petroleum consumed in the United States.

Energy use in each mode of transportation reflects its degree of use as well as its energy efficiency characteristics. Figure 3.1 breaks down total U.S. transportation energy use into components, by mode, for the year 2003. As shown, passenger travel is dominated by automobiles and by air transport for longer distances.² Mass transit and scheduled intercity rail and bus services have important roles in some locations but account for only a small proportion of total passenger-miles.³ On the freight side, the major transport modes are by truck, rail, water, pipeline, and air. Trucking dominates in terms of tons and value of shipments.

In 2006, petroleum accounted for 96 percent of the energy used for transportation; gasoline accounted for 62 percent of the energy used (EIA, 2006).