public and private entities. As a whole, the sector’s activities use about 28 percent of the nation’s primary energy supply (see Figure 4.1), including more than 70 percent of all the petroleum. U.S. transportation is almost entirely dependent on petroleum, 56 percent of which was imported in 2008. Transportation also has environmental impacts. For example, it is responsible for about a third of all U.S. CO2 emissions arising from energy use, as well as for significant fractions of other air pollutants.

Passenger transport is dominated by personal automobiles and aviation.14 (Mass transit and scheduled intercity rail and bus services play important roles in some regions, but overall, they account for a modest proportion of total passenger-miles.) On the freight side, trucking dominates both with respect to tons and value of shipments.15 Thus, highway travel, for passengers and freight alike, is the preponderant mode of transportation in the United States, accounting for about 75 percent of all transportation energy use. Consequently, efficiency gains in highway vehicles will have the greatest effect on the transportation sector’s total consumption of energy.16

The motivators for energy efficiency in commercial transportation differ from those for private transportation. Lifetime operating cost, and thus energy efficiency, is important to companies supplying passenger and freight transportation. The commercial transportation sector is so highly competitive that even small cost differentials among firms can have major impacts on their profitability and growth. In contrast, consumer purchases of motor vehicles are influenced by many factors, including vehicle comfort, style, and operating performance. Historically, vehicle fuel efficiency has not been a major factor in consumer decisions. In addition, although there are many reasons for consumer choice of vehicles, from 1980 until recently U.S. gasoline prices had been falling (after accounting for inflation), which encouraged consumers to buy (and manufacturers to offer) larger, more powerful, and heavier vehicles.

Transportation energy consumption is also influenced by the physical networks of infrastructure through which vehicles move; by the logistic, institutional,


Bureau of Transportation Statistics, National Transportation Statistics. Available at




Nonetheless, other modes, such as mass transit, intercity rail, and water, have important roles to play in bringing about more energy-efficient passenger and freight transportation, particularly if traffic is shifted to them from the more energy-intensive highway and aviation modes.

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