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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
their batteries. These strategies are discussed in Section 2.0, in the context of their
associated fuel requirements.
Much work currently is underway in the area of evaluating the effectiveness and costs of
various vehicle technologies in reducing fuel consumption and greenhouse gas emissions.
The National Academy of Sciences is undertaking a study on light-duty vehicle
technologies that will be available at the end of 2009 and a study on heavy-duty
technologies that will be available in 2010. The National Highway Traffic Safety
Administration (NHTSA) is conducting state-of-the-art vehicle simulations as part of its
analysis for the notice of proposed rulemaking for the 2012-2016 Corporate Average Fuel
Economy (CAFE) standard (NHTSA, 2008a). NHTSA is also working on a study of
medium- and heavy-duty vehicle and work truck fuel efficiency. This Report to Congress
provides information from studies available at the time of writing (generally through June
2009, although some studies released as late as September 2009 are referenced). This
section of the Report to Congress attempts to provide useful information to Congress
regarding the potential of vehicle efficiency strategies to reduce greenhouse gas emissions
in the near, medium, and long terms by citing ranges of effectiveness and costs from the
literature, evaluating technologies against a common baseline, and discussing key
considerations. Key uncertainties and differences between analyses are noted.
Assessing the benefits of any particular strategy or set of strategies is a complicated and
often controversial task that is best done at the time a strategy or set of strategies is being
considered as a path forward. It is also critical to include in such an analysis the best,
most current data and reliable assumptions.
Summary of Impacts
Vehicle fuel efficiency strategies have the potential to generate significant emission
reductions, especially in the medium to long term as the vehicle fleet turns over and new
technology is phased in. 3 The greatest potential exists in the light-duty sector, since it is
responsible for the greatest amount of GHG emissions and also experiences relatively
quick fleet turnover compared to other sectors – with the vast majority of the vehicle fleet
turning over within 15 years, compared to 20 years or more for trucks and up to 40 years
for locomotives, marine vessels, and aircraft. However, each of these strategies is
expected to penetrate the market to some degree on its own without further government
incentives or mandates. Therefore for a given market penetration level, the incremental
emission reductions obtainable from these strategies will be diminished somewhat over
time when compared against a baseline forecast, as opposed to current conditions. 4 Some
3 In this report, “near-term” refers to the 2010-2015 timeframe, “medium-term” to 2030, and “longterm”
to 2050.
4 All comparisons in this section (and throughout this report) are made with respect to the U.S.
Department of Energy (DOE) Annual Energy Outlook (AEO) Reference case forecast through
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