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

Transportation's Role in Reducing U.S. Greenhouse Gas Emissions: Volume 1
older technology (1,014 g/kWhr), at a low battery efficiency of 0.4 kWhr/mile,
PHEVs operating in a charge depleting mode would still result in 12 percent
lower GHG emissions than corresponding conventional gasoline vehicle
operation, on a per mile basis. However, under these extreme circumstances,
PHEV operation will not provide benefits relative to an HEV baseline. 72
Retrofits can be used to speed improvements. Retrofits of heavy-duty trucks to
use aerodynamic fairings, trailer-side skirts, low-rolling resistance tires,
aluminum wheels, and planar boat tails reduce per truck GHG emissions by 10
to 15 percent. For new trucks, combined powertrain and resistance reduction
technologies are estimated to reduce per vehicle emissions by 10 to 30 percent in
2030.
Aircraft advances, including open-rotor engines or blended-wing designs, could
potentially reduce GHG emissions by 10 to 40 percent per aircraft from baseline
conditions, as these technologies are phased in over the next 20 to 30 years. 73
Significant improvements in the efficiency of rail and marine vehicles are also
possible—potentially 20 percent or more with an effective suite of advanced
technologies. However, these sectors’ contributions to total transportation
emissions are relatively small, and the total GHG reductions that may be
achieved are somewhat less than for other sectors. 74
The emission reductions associated with vehicle improvements will start slowly,
but increase over time as new technology is phased in. Fleet turnover varies by
type of vehicle, occurring more quickly in the light-duty sector (where most
vehicles are replaced within 15 years), than for trucks, railcars, and marine
vessels (for which vehicle lifetimes typically range from 20 to 40 years); and
about 30 years for aircraft. Despite the long lifetimes of these vehicles, newer
vehicles tend to be used more than older vehicles (especially in the trucking
sector), and therefore GHG reduction benefits will occur somewhat more
quickly. Some near-term reductions may also be obtained through retrofits of
trucks, railcars and marine vessels.
Technologies to improve vehicle fuel efficiency generally have the effect of
increasing the initial purchase price of the vehicle, or requiring up-front capital
investment in retrofits. However, these technologies also yield cost-savings over
time due to reductions in fuel consumption. Many—including most advanced
gasoline vehicle technologies, truck efficiency improvements, and rail and
marine technologies--yield net cost-savings over the life of the vehicle and can
cover the initial investment within a much shorter timeframe. Others, such as
diesel, hybrid-electric, and plug-in hybrid electric vehicles, have somewhat more
72 Vol. 2 Sec 3.2.
73 Vol. 2 Sec. 3.7.
74 Vol. 2, Sec. 3.5 and 3.6.
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