Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
Figure 2.11 GHG Emissions per Passenger-Mile Traveled (PMT) by Passenger
Transportation Mode
2006
g CO2e/PMT
350
300
250
200
150
100
50
0
Light-duty
Trucks
Passenger
Cars
Aircraft –
Domestic
Passenger Rail Motorcycles Buses
Source: U.S. EPA, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 to 2006; Bureau of
Transportation Statistics. Bureau of Transportation Statistics, National Transportation Statistics;
and U.S. Department of Energy, Transportation Energy Data Book.
Freight modes have very different GHG profiles, as shown in Figure 2.12. On a
ton-mile basis, freight rail is the lowest emission mode, followed by pipelines
and marine transport. These three freight modes specialize in carrying bulk or
containerized goods in large quantities, at relatively slow speeds, and achieve
significant economies of scale. Trucking generates significantly higher GHG
emissions per ton-mile, reflecting the energy inefficiencies of relatively small
vehicles traveling at higher speeds, as well as the lighter weight of its cargo.
Aircraft, which primarily carry high-value, time-sensitive cargo, have by far the
highest GHG emissions per ton of freight. 49 However, because of the different
mix of traffic that the modes carry, a head-to-head comparison between modes—
based purely on tonnage—may not present a complete picture. A more
appropriate comparison would be to consider the energy consumption of the
different modes moving similar traffic within specific corridors. For instance, a
FRA study compared rail and truck fuel efficiency by focusing on corridorspecific
competitive services that each mode provides. Overall, the study found
that rail achieved 1.4 to 9 times more ton-miles per gallon than competing
truckload service. An update to this study finds that rail-fuel improvements
have outpaced truck-fuel improvements over the study period. 50
49 Including freight carried in the belly of passenger aircraft.
50 U.S. Department of Transportation, Federal Railroad Administration, 2009 (cited).
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