U.S. Department of Energy - Energy Efficiency and Renewable Energy

Energy Analysis

Energy Intensity Indicators: Transportation Total Energy Consumption

This section contains an overview of both the aggregate transportation sector and the two major subsectors. For further detail within the transportation sector, see the Trend Graphics or download the appropriate Trend Data worksheet.

Results are presented based on total energy consumption for the period between 1985 and 2004.

  • Activity: Aggregate transportation activity (as measured by weighted average of passenger-miles and freight ton-miles) increased 55%.
  • Energy Use: Transportation energy use increased by 42%.
  • Energy Intensity Index: Energy intensity over this period declined 14%. Figure T1, below, shows these trends from 1985 through 2004.
  • Changes due to factors unrelated to efficiency improvements: The two major subsectors that make up the transportation sector are passenger movement and freight transportation. Within each of these subsectors there have been shifts between highway transport and other modes (air, rail, and water). In the passenger transportation subsector, there has been a dramatic change in the mix of vehicles, with light-duty trucks (e.g., SUVs) increasing their market share over automobiles. In transportation, these shifts are the major "other explanatory factors," that were introduced in the economy-wide indicators. The net impact of these shifts in the mix of transportation modes (called "modal shifts") has contributed to higher energy consumption. As the graph below indicates, the overall impact of these shifts is estimated to have increased transportation energy use by about 7% over the period.
A chart shows four lines representing aggregate transportation activity, total energy use, energy intensity index, and the net impact of shifts in the mix of transportation modes, called "modal shifts," for the years 1985 to 2004.  An index with 1985 equal to 1.0 is plotted on the vertical axis; years are plotted on the horizontal axis.  The top line, aggregate transportation activity, rises fairly steadily from 1.0 to 1.55.  The second line from the top, transportation total energy use, rises fairly steadily—except for a slight dip in 1991—from 1.0 to 1.42.  The third line from the top, modal shifts, rises only slightly, reaching 1.07 in 2004.  The fourth line, energy intensity, is at 1.0 in 1985 and 1986, then drops with a slight undulation, reaching 0.86 in 2004.  All lines show very gradual changes throughout the period.

Figure T1. Total Transportation Activity, Intensity, Energy Use and Modal Shifts, 1985-2004

Passenger Transportation - Total Energy

  • Activity: Since 1985, passenger-miles traveled have increased 59%.
  • Energy Use: Energy use has increased over 38%.
  • Energy Intensity Index: The energy intensity index declined by 14.4% from 1985 to 2004, as shown in Figure T2. Much of that decline occurred prior to 1992. The flattening of this decline in the past decade is largely due to a slowing in the decline in average fuel economy (miles-per-gallon) of automobiles and light-duty trucks.
  • Changes due to factors unrelated to efficiency improvements: Modal shifts in passenger transport, primarily between highway and air transportation, have reduced energy use slightly (on an energy per passenger-mile basis, air travel is less energy-intensive than highway travel). The most significant development has been the changing mix between light trucks and passenger cars. This trend has contributed to about a 2% increase in overall passenger energy consumption since 1985.
A chart shows four lines representing passenger transportation activity, total energy use, energy intensity index, and the net impact of shifts in the mix of transportation modes, called "modal shifts," for the years 1985 to 2004.  An index with 1985 equal to 1.0 is plotted on the vertical axis; years are plotted on the horizontal axis.  The top line, activity index, gradually rises from 1.0 to 1.59 in 2004.  The next line, energy use, rises to a peak of 1.1 then falls back to near 1.0 in 1991, then rises at roughly the same rate as the top line, reaching 1.38 in 2004.  The third line from the top, modal shifts, barely rises above 1.0 during the period, and the only drop is a tiny one in the last year, finishing at 1.02.  The bottom line, energy intensity index, stays at or near 1.0 until 1989, then gradually drops to about 0.85 in 2004.  All lines show gradual changes throughout the period.

Figure T2. Passenger Activity, Intensity, Energy Use, and Modal Shifts, 1985-2004

Passenger Transportation Mode Shifts

To better see how the various types of modal shifts have offset each other, the total modal shift is shown in the Figure T3 below, plotted with the modal shift at this aggregate level and the cumulative shifts at lower subsector levels (these indices are plotted on a scale that exaggerates the shifts; note that the index limits fall into about a 5% range). The modal shifts at the aggregate passenger transportation level have contributed to about a one-half percent reduction in energy use between 1985 and 2004 as a result of a changing distribution of passenger-miles between highway, air, and rail transportation. The cumulative effect of modal shifts within the highway, airline, and rail categories (primarily attributed to changes in the mix of vehicles), however, increased energy use by 2.2%. When these indexes are combined, the result is the structural change labeled "Total Structure," and is the net effect (+1.7%) of all of the "other explanatory factors."

The modal and vehicle-mix shifts at the detailed passenger subsector levels are shown in more detail on the Trend Graphics page, or in the downloadable Transportation Data file. These links provide more detail for highway transportation (personal vehicles [autos and trucks] and busses), urban and inter city rail, and air passenger travel.

A chart shows three lines representing modal shifts, vehicle choice, and total structure for the years 1985 to 2004.  An index with 1985 equal to 1.0 is plotted on the vertical axis; years are plotted on the horizontal axis.  The top line, vehicle choice, and the second line, total structure, both drop in the first year to 0.997, then climb above 1.0 in 1987 and move in an undulating fashion fairly closely together until 2003, with the vehicle choice line always slightly above the total structure line.  The vehicle choice line rises to just above 1.020, and total structure reaches just below 1.020 in 2003.  In the last year, the two lines diverge, with the vehicle choice line moving upward to 1.022, while the total structure line falls to 1.017.  The total modal shifts line is nearly flat at or near 1.0 until 1993 when it gradually drops to 0.996 by 2000; then it rises and falls like the top of a ball, reaching nearly 1.0 in 2002 and dropping to 0.995 in 2004.

Figure T3. Passenger Structural Changes: Mode Shifts and Lower Level Effects, 1985-2004

Freight Transportation - Total Energy

  • Activity: Freight activity, measured in ton-miles traveled, increased over 43% between 1985 and 2004.
  • Energy Use: Energy consumption grew nearly 53% over the same period.
  • Energy Intensity Index: Freight transportation energy intensity decreased by almost 14%. Most of this decline occurred between 1985 and 1998. Since 1999, the index has fallen by less than 2%.
  • Changes due to factors unrelated to efficiency improvements: As shown in Figure T4, both modal shifts at the aggregate level (e.g., shifts between air freight and truck freight) and activity increases have contributed to higher energy consumption, while intensity changes have slightly reduced energy use. Modal shifts account for a nearly a 23% increase in energy consumption over this period. Much of this shift is due to a greater fraction of freight ton-miles being carried via truck and air, as compared to water, rail, and pipelines.
A chart shows four lines representing energy use, activity index, modal shifts, and energy intensity for the years 1985 to 2004.  An index with 1985 equal to 1.0 is plotted on the vertical axis; years are plotted on the horizontal axis.  The top line, energy use, gradually rises from 1.0 in 1985 to 1.53 in 2004.  The second line from the top, activity index, is always slightly below the top line, rising from 1.0 to 1.43 over the time period.  The third line, modal shifts, rises from 1.0 to nearly 1.23 over the time period.  The fourth line, energy intensity, stays around 1.0 in 1986 then slowly drops, reaching about 0.85 in 2004.  All lines show gradual changes throughout the period.

Figure T4. Figure T4. Freight Activity, Energy Use, Intensity, and Modal Shifts, 1985-2004