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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Low-viscosity engine and transmission fluids exist that can reduce parasitic driveline
losses. Limitations to these fluids include convincing operators to pay for the higher costs
as part of their maintenance cycle, and uncertainty regarding long-term effects on
component durability (Killian, 2008).
In the case of improvements to fuel injectors, intakes, and turbocharger design, fuel
consumption and emissions can often be reduced together. There is a limit to the
improvements that allow these two characteristics to move in the same direction,
however, and it is estimated that engines could achieve 15-20 percent higher fuel
efficiency using today’s technology if there were no NOx requirements. Accordingly, fuel
efficiency also could be significantly improved with a breakthrough in NOx
aftertreatments which could allow engines to operate at their most efficient levels without
regard for engine-out NOx levels (Greszler, 2006).
As mentioned previously, heavy-duty hybrid market penetration is several years behind
the current level in the light-duty marketplace. Many issues exist that present challenges
before heavy-duty hybrids can gain a foothold in the market. For example, electrical
components such as air-conditioning and steering pumps only exist as expensive
prototypes in heavy-duty vehicles—there are no widely available systems yet that can
sustain regular heavy-duty duty-cycles. In addition, optimized engines, more advanced
combustion schemes, and lighter weight materials are necessary for heavy-duty hybrid
technology to reach maturity (ATA, 2006). Finally, battery replacement costs have not
been included in the above analysis, and may be substantial, assumed by one source to be
required approximately every six years (NESCCAF/ICCT, 2009).
Advanced integrated aerodynamic improvements will require a redesign of the tractortrailer
system in order to minimize overall drag. This strategy is particularly challenging,
given the lack of incentive on the part of trailer owners, who would not normally see a
monetary benefit associated with their (quite sizable) investment.
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