FIGURE 7.1 The rise in passenger vehicle miles traveled (VMT) since 1970 in the United States closely tracks increasing incomes but well exceeds population gains. In the United States, passenger VMT in 2005 was more than 2.5 times VMT in 1970 whereas population grew by a factor of only 1.5. Worldwide, passenger travel (kilometers traveled) more than quadrupled between 1960 and 1990 and is expected to more than quadruple again by 2050 (Schafer and Victor, 2000). NOTE: “Trucks, combination” combines all vehicles with two or more units, one of which is a tractor or straight truck power unit. Miles-traveled statistics are for highway travel. SOURCES: Passenger VMT data from National Transportation Statistics, Table 1-32; population statistics from U.S. Census Bureau (2007), Table 2; combination truck statistics from Federal Highway Administration (annual series), Table VM-1.