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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
On-road heavy-duty vehicle strategies can provide significant GHG reductions as well,
beyond efficiency improvements already considered in baseline projections. Unlike most
vehicle strategies evaluated here, retrofits of heavy-duty trucks (including aerodynamic
fairings, trailer side skirts, and low-rolling resistance tires, among others), particularly
long-haul freight trucks, can provide significant reductions in the near term. Most of these
technologies currently are available. Significant additional reductions in the medium to
long term are possible for engine and powertrain modifications that require time to
penetrate the fleet. Examples of emerging powertrain technologies include
turbocompounding, bottoming cycle, and hybridization. Some of these technologies are
proven and are beginning to penetrate the market (such as hybridization), while others
(such as bottoming cycle) require further research and demonstration. Per vehicle costs
can be sizeable, at least $10,000 for aggressive tractor and trailer retrofits, to over $20,000
per unit for a full suite of retrofit, engine, and powertrain improvements using
conventional technologies, or over $60,000 using advanced technologies on large (Class 8)
trucks. Most of these improvements yield net cost savings over the lifetime of the vehicle
due to fuel savings, assuming baseline AEO fuel price projections.
Bus strategies, including hybridization and fuel cells, offer substantial reductions on a per
vehicle basis. However, the entire bus sector, including transit buses, school buses, and
intercity buses, is responsible for less than 1 percent of total on-road GHG emissions in the
U.S (about 20 mmt CO2e). As such, no strategy offers more than modest reduction GHG
potential, with benefits and costs only addressed qualitatively in this section. While
technology options are generally available, capital costs currently are high due to low
production volumes and other factors, although initial costs will be at least partially
recouped over time through operating cost savings.
GHG reductions are possible through the use of genset and hybrid locomotives in rail
yards (35 to 60 percent per locomotive), as well as through improvements to line-haul
locomotives and train sets, including more efficient line-haul locomotives (10 to 20 percent
improvement), lightweight cars, aerodynamic improvements, wheel-to-rail lubrication
technologies, and drive system operation (22 to 31 percent combined improvement per
train). All of these technologies are commercialized and available for immediate use,
although some must be phased in over time as fleet turnover occurs. While incurring
higher up-front capital costs, most of these strategies have the potential to pay for
themselves in less than 10 years through fuel cost savings.
Improvements to marine vessel design can reduce fuel consumption and GHG emissions
by 2 to 35 percent per vessel. Changes to propulsion systems (such as diesel-electric or
hybrid systems) can have a similar impact for vessels that vary their operations frequently
such as harbor vessel, cruise ships and vessels involved in short sea shipments. Changes
in propeller design can improve efficiency by 4 to 15 percent while solar photovoltaic
technologies can provide a fuel savings and GHG reduction of 5 to 7 percent. In the
longer term, application of devices that utilize wind power to supplement vessel energy
supply may provide fuel savings between 5 and 30 percent for long-distance vessels. All
of these technologies are commercially available, although solar photovoltaics are still
expensive and wind power remains in the demonstration stages. While some
technologies (such as propeller designs and solar panels) can be retrofit on existing vessels
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