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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
the enactment of the EISA, with this criteria applicable to both domestic and foreign
producers of renewable fuels.
Life-Cycle Analyses
The life-cycle greenhouse gas impacts of a fuel – not just emissions from the vehicle itself –
must be considered when evaluating low-carbon fuel options. The GHG emissions
resulting from vehicle operation (i.e., “tailpipe” emissions) are only a part of the total lifecycle
emissions associated with transportation fuel use. As depicted in Figure 2.1, a lifecycle
analysis takes into account the GHGs associated with the extraction, processing,
distribution, and dispensing of the fuels (Winebrake et al., 2001).
Figure 2.1 Life-Cycle of a Transportation Fuel
Feedstock-Related Stages:
Feedstock recovery,
transportation, storage,
distribution of feedstock
Fuel-Related Stages:
Fuel processing,
transportation, storage,
distribution of fuel
Vehicle Operation:
Refueling and
operation
Upstream Downstream
Note: “Upstream” also is known as “well-to-pump” and “downstream” as “pump-to-wheel,” with
the full cycle known as “well-to-wheel.” Vehicle operation includes tailpipe emissions from
combustion of the fuel in the vehicle’s engine, as well as any emissions associated with
refueling the vehicle.
The analysis contained in this report considers “well-to-wheel” emissions, which includes
all three stages shown in Figure 2.1. Fuel combustion is responsible for about 80 percent of
the life-cycle GHG emissions for petroleum fuels, while the processes from feedstock
extraction through fuel delivery (well-to-pump) account for about 20 percent. Some GHG
emissions also are associated with vehicle manufacture and disposal; these would add
about 10 percent to the emissions total but are not included in this analysis, which focuses
only on fuels. 2
2 Certain advanced technology vehicles require higher energy intensity materials, entailing a slight
increase in manufacturing emissions (increasing from about 26 g GHG per mile traveled for
conventional vehicles to about 30g per mile for fuel cells and battery electrics – Heywood et al.,
2008).
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