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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
1 to 14 percent (U.S. DOE, 2007), although they are not expected to appear in the market
for a number of years, and are not included in the AEO Reference case.
Vehicle technology improvements such as lower weight, reduced drag, and reduced tire
friction are estimated to have the ability to reduce fuel consumption by 6 to 9 percent in
the near term, and by a total of 10 to 13 percent in the long term (NRC, 2008). AEO
projections estimate close to 100 percent penetration of some form of these technologies by
2030. It is estimated that a vehicle weight reduction of 10 percent can result in a 3.3 to
8 percent reduction in fuel consumption for a light-duty vehicle (NHTSA, 2009b;
Bandivadekar et al., 2008). The benefit is greatest for the least efficient and heaviest
vehicles.
While many of the technologies discussed here are not expected achieve 100 percent
market penetration, most are expected to be commercially viable in the near term. A
recent study performed for EPA estimated most technology options discussed above will
attain technical “production readiness” (if not market penetration), within five years, with
HCCI requiring up to 10 years (U.S. EPA, 2008b). Generally speaking, advanced
combustion engine design features, along with hybrids, are expected to incrementally gain
market penetration without incentive programs or other market interventions.
It also is important to note that the fuel economy benefits of these different measures are
not purely additive, and integrated packages of these technologies will produce somewhat
lower improvements than the sum of the individual measures.
Combined Per-Vehicle Benefits
Various estimates have been developed regarding the fuel consumption and CO2
reduction potential of different technology packages. Studies conducted by the National
Academy of Sciences and the Northeast States Center for a Clean Air Future estimated
CO2 reduction potentials from 24 to 30 percent for large SUVs, and 17 to 29 percent for
midsized cars (U.S. EPA, 2005). A more recent assessment conducted for EPA estimated
fuel consumption and CO2 reduction potentials between 22 and 30 percent for selected
packages, depending on vehicle class. These packages also were estimated to have
roughly similar performance levels compared with conventional gasoline vehicles (U.S.
EPA, 2008b). The AEO Reference case assumes a 22 percent CO2 reduction potential for
passenger cars and a 24 percent reduction for light trucks and SUVs occurring between
2008 and 2030.
For advanced conventional light-duty vehicles, the technology packages found in
literature frequently do not contain the same group of technologies. Therefore, a group of
improvements for advanced gasoline vehicles was chosen for evaluation. These
technologies represent those identified most often in the literature evaluating advanced
gasoline LDV systems. In the long term, they represent almost all of the foreseeable
improvement in fuel economy available to conventional gasoline engines. In the medium
and long term, these technologies include the maximum foreseeable accessory
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