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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
effective replacements for conventional gasoline LDVs, now and into the future.
However, it is instructive to consider the cost-effectiveness of HEVs from the perspective
of advanced gasoline vehicle systems, above and beyond those assumed for the AEO
Reference case baseline vehicle. For example, one evaluation estimated the incremental
cost of full hybrids relative to “maximum ICE improvements” to be 22 percent, but the
associated fuel consumption benefit was estimated to be only 5 percent beyond the
maximum ICE level (McKinsey, 2009, page 97). As such, additional investments in
moving from advanced gasoline vehicles (see Section 3.3) to HEVs will suffer from
diminishing returns as the potential for incremental GHG reductions decreases.
Cobenefits
HEVs generally have lower criteria and toxic emissions than comparable conventional
gasoline LDVs, resulting from lower fuel consumption and engine-on time, better engine
load management, and generally smaller engines, among other factors. HEVs may meet
more stringent emission standards than those currently required of conventional LDVs,
particularly, California’s most stringent Partial Zero Emission Vehicle (PZEV) standard
(JDPower, 2009). Variation across the different available models make it difficult to
quantify criteria pollutant reductions for HEVs as a whole, however.
HEV brake maintenance costs for HEVs with regenerative braking are expected to be
lower than conventional vehicles, about $400 to $500 over the vehicle life (EPA, 2005). The
longer range of LDV HEVs results in decreased refueling times. Otherwise, performance
characteristics of HEVs are generally similar to that of conventional gasoline vehicles.
Feasibility
HEVs are now penetrating the LDV market, with the number of models increasing each
year. Although initial concerns regarding battery life were expressed, current nickelmetal
hydride (NiMH) batteries and other hybrid system components are commonly
covered by 8-year/100,000 mile warranties, and 90 percent of HEV battery packs are
anticipated to survive 14 years (EPA, 2005).
The overriding issue facing HEVs today focuses on their cost, primarily battery costs. The
literature on the subject assumes advancements will likely continue to be made in terms of
cost, size, weight, charge capacity, and longevity. Current HEVs use NiMH batteries,
although research is being performed regarding lithium ion (Li-ion) batteries because of
their greater charge density (which can provide greater vehicle range per unit weight),
and lower cost potential. Li-ion batteries currently are expected to enter production in
some HEVs over the next two years, although they are not yet as stable as current NiMH
batteries, with some Li-ion systems involved in recalls in the consumer electronics market.
If overcharged or overheated, these batteries have been known to catch fire in the past
(Kromer and Heywood, 2007). However, several researchers have concluded that the
remaining technical difficulties associated with Li-ion performance are likely to be solved
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