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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
and realize short-term benefits, most must be phased in with new vessels. The rate at
which benefits are realized will be limited by the slow turnover rate of the commercial
marine fleet, where vessels may remain in service for 30 to 40 years or more. All are
expected to lead to net cost savings of the life of the vessel.
Use of new aircraft engine technologies such as improved current engine design, geared
jet, and open rotor engines can provide an improvement in fuel consumption and
reduction in GHG emissions (10 to 15 percent, with potentially up to 30 percent for openrotor,
compared to current aircraft). In the medium to long term, reductions of 20 to
30 percent may be possible on larger aircraft through the use of the blended wing body
design. With the exception of improvements to the current engine design, which are
commercially available, these other aircraft options may be available in the near future (5
to 10 years). On a fleet-wide basis, both aircraft engine and airframe technology
improvements could potentially increase fuel consumption efficiency by 1.4-2.3% annually
between 2015–2035 relative to 2015 as the base year.
Vehicle air conditioning (A/C) system measures offer modest to moderate GHG
reduction potential. Adoption of a “can-ban” eliminating the practice of do-it-yourself
servicing, or a deposit program for small refrigerant cans, could be implemented in the
near term, These systems have been demonstrated in various test studies, but are not yet
commercially available. A/C system loads also can be reduced (lowering GHG emissions
by reducing main engine loads) through the adoption of reflective glazing (to lower cabin
temperatures), and adoption of other A/C system modifications. Per unit costs for
alternative refrigerant systems are expected to be relatively low at full production (less
than $100 per vehicle), although the costs incurred for professional servicing under a canban
can be several hundred dollars over the life of the vehicle; the cost-effectiveness of
alternative refrigerants is estimated to be in the range of $40 to $90 per tonne CO 2e.
The Rebound Effect
Benefits from technology strategies may be somewhat offset due to the “rebound effect.”
This effect can be characterized as the extent to which fuel savings (and corresponding
GHG reductions) from vehicle fuel efficiency improvements are offset by increased travel,
because travel is made cheaper per-mile due to reduced fuel costs. The National Highway
and Traffic Safety Administration used a 10 percent rebound effect in its analysis of fuel
savings and other benefits from higher CAFE standards for MY 2012–2016 vehicles.
Recognizing the uncertainty surrounding the 10 percent estimate, the agency analyzed the
sensitivity of its benefits estimates to a range of values for the rebound effect from 5
percent to 15 percent. (NHTSA, 2009). (For more detail on the rebound effect, see
Appendix A.)
The impact of the rebound effect is fairly straightforward to demonstrate in the case of
strategies that improve the efficiency of existing gasoline or diesel vehicles. For example,
if advanced gasoline technology improved fuel efficiency by 20 percent, a 15 percent
rebound effect would reduce the overall fuel savings and GHG reduction benefits by
3 percent (15 percent of 20 percent), to 17 percent. For efficiency improvements that
involve the use of different fuels (such as switching from gasoline to diesel or PHEVs that
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