Passenger travel was 1.0 percent more energy efficient in 2001 than in 1991. During the same period, however, freight energy efficiency declined by 5.4 percent1 [1, 2].
Improvements in domestic commercial aviation are the primary reason for the gains in passenger travel efficiency (figure 15-7). For instance, improved aircraft fuel economy and increased passenger loads resulted in a 26 percent increase in commercial air passenger energy efficiency between 1991 and 2001. Domestic commercial air pmt rose 44 percent during this same period, while energy consumption grew only 14 percent .
Highway passenger travel—by passenger cars, motorcycles, and light trucks2—represented 86 percent of all pmt and 91 percent of passenger travel energy use in 2001. Overall, highway travel was 1.0 percent less efficient in 2001 compared with 1991. This loss was due to a 4.3 percent decrease in the efficiency of light trucks. For the period 1991 to 2001, light truck pmt increased 34 percent, while energy use rose 39 percent. On an annual average basis, the decline in light truck energy efficiency is due to a 2.9 percent rise in pmt coupled with a faster average annual increase of 3.4 percent in energy consumption during this period. Meanwhile, passenger car pmt rose 17 percent and motorcycle pmt declined 10 percent. Total highway passenger pmt grew 22 percent .
The decline in freight energy efficiency between 1991 and 2001 resulted from a 1.8 percent average annual growth rate of ton-miles paired with a 2.4 percent average annual growth rate in freight energy consumption (figure 15-8). Contributing to this trend was a decline in the energy efficiency of freight trucks (–1.8 percent), pipelines (–4.0 percent), and waterborne transportation (–13 percent). However, during the same period, rail and air freight energy efficiency increased by 13 percent and 9 percent, respectively .
1. American Public Transportation Association, Public Transportation Fact Book 2003 (Washington, DC: 2003), tables 33 and 35.
2. U.S. Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 2003, calculations based on tables 1-34, 1-44, 4-6, and 4-8, available at http://www.bts.gov, as of March 2004.
1 Passenger energy efficiency is measured in passenger-miles of travel (pmt) per British thermal unit (Btu). Freight energy efficiency is ton-miles per Btu.
2 Light trucks include minivans, pickup trucks, and sport utility vehicles.