As mentioned in Chapter 5, the U.S. automotive market is mature; to a very large extent, consumers purchase new cars to replace cars that have worn out. Figure 6-1 shows the additions and subtractions (sales and scrappage) of cars and light trucks in the United States between 1970 and 1989. The scrappage numbers represent automobiles, trucks, and buses, with automobiles accounting for about 80 percent in 1989. Throughout the period, the ratio of licensed drivers to automobile registrations remained virtually unchanged at a value of 1.2; the ratio of licensed drivers to automobiles on the road has changed from 1.37 in 1978 to 1.34 in 1989 (Motor Vehicle Manufacturers Association [MVMA], 1991). Figure 6-2 shows registrations and automobiles on the road in recent years, as well as the U.S. population between 16 and 65 years of age, historically and projected through 2020. The size of the latter group-approximately the set of licensed drivers—is projected to grow from 1991 to 2010, level off at 2010, and then decline.