FIGURE 4.1 U.S. light-duty vehicle fuel efficiency and performance trends from 1975 to 2005. NOTE: Three-year moving average, used to smooth curves, means that for each year, what is shown is the average of that year with the two previous years. SOURCE: EPA (2006).

there were major increases in the use of plastics and aluminum, the highest percentage new material introduction was high-strength steel. Since 1980, vehicle efficiency has continued to improve even as air pollution laws and regulations have tightened, forcing vehicle designers to accommodate a multiplicity of goals. Engines, transmissions, drivetrain components, and vehicle aerodynamics have all improved remarkably, with these improvements spread among emissions reduction, improved performance, greater weight, and more power-consuming accessories in the cabin (EPA, 2005).

Since 1987, only a small fraction of these improvements have been directed to fuel economy, as shown in Figure 4.1 (EPA, 2006). After an initial marked drop in average vehicle weight and a significant fuel economy increase, most of the continuing improvement in power train technology went to overcome a steady increase in vehicle weight and to provide enhanced performance, particularly faster acceleration. The baseline case projects this trend to continue into the future because it is driven by consumer choices similar to those that have been made over the past 20 years. Although some changes in motorist attitudes can be expected, driven by higher fuel prices and an enhanced environmental consciousness, they are unlikely to produce radical improvements in light-duty vehicle fuel efficiency. However, suitable policies promoting fuel efficiency could change vehicle design priorities and result in significantly improved vehicle fuel efficiency, leading to reductions in oil imports and CO2 emissions.

During the same period in Europe, major advances have been made in compression-ignition (diesel-fueled) engines; today, such engines form a major part of Europe’s CO2 reduction efforts. There is concern about NOx and particulate emissions from diesel engines, and the standards for these emissions have been tightened, as have the specifications on diesel fuel to enable effective emission control technologies. This activity has resulted in the development of new after-treatment devices for NOx and particulates for diesel engines. These technologies continue to improve.

In 1997, the hybrid electric vehicle was introduced in Japan and, in 2000, imported to the United States. In 2006, 364,845 HEVs (with 254,545 in the United States) were sold worldwide out of 68,727,429 total global vehicle sales. The National Research Council (NRC) report on the hydrogen economy and fuel cell vehicle, which was released in February 2004 but had access only to actual year-end 2002 HEV sales numbers, projected that 2006 HEV sales in the United States would represent 2 percent of the market and would increase 1 percent annually thereafter for the next 9 years and 5 percent per year for the next 10 years (NRC, 2004). The actual 2006 U.S. sales were 1.5 percent. As shown in Figure 4.2, even though gasoline prices have fluctuated dramatically from 2004 to the present, the actual increase in sales was less in 2006 than in 2005 (DOE, 2007).

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