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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Apart from the primary benefits of increased fuel efficiency and reduced GHG emissions,
widespread market penetration of HD hybrids is likely to result in marked reduction in
both PM and NOx emissions resulting from reduced diesel fuel consumption. Initial test
results for hybrid electric buses, for example, have shown NOx reduction of 50 to
60 percent, with corresponding PM reduction of greater than 90 percent, relative to pre-
2007 diesel engines (ATA, 2006). For 2010 diesel engines, where tailpipe emissions will be
just a few percent of uncontrolled levels, the benefit will be much less significant.
Feasibility
The engine and powertrain improvements discussed in this section typically need to be
designed into a new vehicle, and therefore are not feasible for retrofit on existing vehicles
(unless an entirely new engine is retrofit to a vehicle). As such, policy needs will be
somewhat different than for resistance reduction strategies, many of which can be retrofit.
One approach is to establish efficiency standards, as currently is being evaluated pursuant
to the EISA of 2007. Given that market economics likely play a larger role in vehicle
purchase decisions for heavy-duty vehicles relative to light-duty vehicles, due to the high
contribution of fuel costs to total operating costs, the adoption of standards may have
relatively less impact. On the other hand, as noted in the previous section, there is
evidence that trucking companies base their purchasing decisions on low amortization
periods of about three years, meaning that even cost-effective strategies will not
necessarily be implemented through market forces alone.
Financial incentives such as tax credits or low-interest loans also may play a role in
helping to overcome initial capital costs. Such incentives are beginning to emerge at the
Federal and State levels to promote the introduction of heavy-duty hybrid technology into
the fleet. For example, the Energy Policy Act of 2005 includes tax credits of up to $12,000
based on the fuel efficiency and weight of a particular vehicle. Finally, demonstration
projects and information dissemination, as performed under EPA’s SmartWay program,
may play a role in helping to inform truck owners about the benefits of new technology
and encourage purchase of more efficient vehicles. Partnerships with larger fleet
operators, for example, may be valuable in bringing a particular technology to scale and
reducing costs such that smaller operators also will be willing and able to adopt it.
Many of these strategies face technical hurdles as well. The turbocompounding and fuel
injection developments noted above are expected to be developed further and increase
their market penetration in the future. They are limited primarily by cost and the
development time needed to ensure that they maximize efficiency and pollutant
reduction. Bottoming cycle systems face tremendous engineering hurdles involving
freeze prevention, vibration, and numerous other factors before they can be considered a
viable option for the on-road market. For example, due to the poor transient response of
the bottoming cycle, this system may have to be coupled with hybrids to achieve
acceptable performance (NESCCAF/ICCT, 2009). Thermoelectrics face cost and durability
issues. Additionally, these devices are not yet efficient enough to provide significant
electric generation.
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