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

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
transportation life cycle, increasing GHG emissions by up to 50 percent more
than operating emissions alone.
GHGs from these three supporting processes appear to be of comparable
magnitude, with fuel cycle emissions likely having the largest contribution. Fuel
cycle processes include the extraction, shipment, refining and distribution of fuel,
and GHGs from these activities vary by fuel type. 54 Gasoline fuel cycle processes
are the most GHG intensive of any conventional transportation fuel, with fuel
cycle processes producing GHGs that are roughly 24 to 31 percent beyond the
combustion emissions of the fuel itself. Diesel fuel cycle emissions are roughly
15 to 25 percent beyond direct diesel combustion emissions, while jet fuel is 17 to
24 percent beyond combustion emissions. 55
Vehicle manufacture cycle emissions include raw material production, vehicle
construction and shipment. GREET and LEM provide estimates of GHGs from
these processes for on-road vehicles; additional estimates are provided by
Chester (2008). With these estimates expressed relative to combustion emissions,
the manufacture-cycle GHGs represent an additional 14 to 19 percent beyond
gasoline combustion emissions; manufacturing of freight trucks is 6 to 17 percent
beyond combustion diesel combustion emissions; and aircraft up to 6 percent.
As shown in Figure 2.14, the EPA estimates that greenhouse gas emissions for
light-duty vehicles are 38 to 50 percent higher than operating emissions alone
when fuel cycle and vehicle cycle emissions are also included. For dieselpowered
freight trucks, emissions are 21 to 45 percent greater when including
fuel cycle and vehicle cycle emissions.
54 Estimates have been developed for Argonne National Laboratory’s GREET model, as
well as for the Life-Cycle Emissions Model (LEM) developed by Mark Delucci at the
University of California at Irvine.
55 U.S. Environmental Protection Agency (2006). Greenhouse Gas Emissions from the U.S.
Transportation Sector: 1990-2003.
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