FIGURE 1-4 Fuel economy (miles per gallon) of passenger vehicles, light trucks, and heavy-duty trucks (more than 10,000 lb), 1973-2005. SOURCE: DOE, EIA, 2007.

FIGURE 1-5 Energy use by the U.S. transportation sector, 1949-2005. SOURCE: DOE, EIA, 2007.

FIGURE 1-6 U.S. petroleum production and net imports, 1949-2005 (thousands of barrels per year). SOURCE: Data from DOE, EIA, 2006, Annual Energy Review 2006, Washington, D.C., Table 5.1

efficiency of heavy-duty diesel engines while, at the same time, achieving the increasingly stringent 2010 emission standards (discussed in Chapter 3 and in Appendix D).

The progressively more stringent federal emission standards for light-duty vehicles are illustrated in Figure 1-7 (Ehlmann and Wolff, 2005). In the early 1960s, when exhaust emissions were unregulated, the subsequent exhaust emission regulations adopted by model year 2004 had reduced exhaust emissions from light-duty vehicles by the following amounts, based on certification-test emission levels (EPA, 2000):

• Hydrocarbons (HC), by 99 percent

• Carbon monoxide (CO), by 96 percent

• Oxides of nitrogen (NO_x), by 99 percent

The control of emissions from the engines of heavy-duty trucks with GVWR over 8,500 lb began in 1973 in California, and in 1974 in the United States as a whole (Johnson, 1988). As shown in Figure 1-8, the progressively more stringent emission standards for heavy-duty diesel engines followed trends similar to those for light-duty vehicles.

FIGURE 1-7 Historical trend in exhaust emission standards for light-duty vehicles, by model year. (The committee combined individual emission standards for hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NO_x) for illustration purposes.) SOURCE: Data from Ehlmann and Wolff (2005).

FIGURE 1-8 Historical trend in federal exhaust emission standards for heavy-duty diesel engines, by model year (in grams per brake-horsepower-hour (g/bhp-h), 1970-2010. HC, hydrocarbons; NMHC, nonmethane hydrocarbons. SOURCE: DOE, 2006a.