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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
85 percent of these vehicles in the light-truck category. 15 Because of their higher engine
weight and power output, they offer the greatest benefit to larger vehicles. Thirteen diesel
passenger car and light-truck models currently are offered for sale in the United States
(Diesel Technology Forum, 2009), although numerous models are available in Europe and
elsewhere around the world. In fact, diesel vehicles represented over 50 percent of new
European purchases in 2007 (Dieselnet.com, 2008), as a result of higher gasoline prices,
favorable taxation policies, and less stringent NOx and PM emissions standards.
However, late model European diesel vehicles would have to achieve a 45 to 65 percent
reduction in NOx emissions in order to meet current United States Tier 2 emission
standards (NHTSA, 2009b).
Accordingly, utilizing diesel engines instead of their gasoline counterparts in the same
application should result in reduced fuel consumption and GHG emissions.
Unfortunately, current diesel engines produce higher NOx and PM emissions than do
today’s advanced gasoline engines, and generally cannot meet the stringent Tier 2 and
California LDV emission standards without advanced treatment technologies. While such
advanced pollutant control options exist, they are frequently costly and may reduce
engine efficiency along with emissions. The analysis in this section assumes that such
pollution control technologies advance so that diesel is a widely viable alternative for
light-duty vehicles. Some of the emission control technologies have minor impacts on fuel
efficiency, but not to the extent that the GHG benefits of diesel are greatly reduced.
Diesel vehicles also can benefit from many of the same technologies described in
Section 3.2 to improve the efficiency of gasoline vehicles, particularly weight reduction,
aerodynamics, transmissions, and electrical systems.
Magnitude and Timing of GHG Reductions
Benefit per Vehicle
For the near term, the analysis focuses on benefits that are possible with substitution of
gasoline vehicles with diesel vehicles using today’s technology. In the medium and long
term, the analysis assumes substitution with advanced diesel engine and vehicle
technologies (including many of those adopted for gasoline vehicles) that represent the
most efficient foreseeable options. Table 3.2H lists the technologies included in the
analysis of diesel vehicles. Many of the vehicle technologies are described in detail in
Section 3.2.1.
15 AEO 2009, Supplemental Table 58.
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