Source: US Department of Transportation, Federal Highway Administration, http://www.fhwa.dot.gov/ohim/tvtw/tvtpage.cfm

Annual Vehicle-Miles Traveled in the United States and Year-over-Year Changes, 1971-2008

The growth of vehicle-miles traveled within the United States was punctuated by sharp periods of decline corresponding to recessions. The drops attributed to the first (1973-74) and second (1979-80) oil shocks were particularly pronounced. However growth rates resumed immediately afterwards to their previous levels. The overall growth trend has steadily been declining, which is common in all diffusion processes as they move towards maturity. Since 2006, growth stopped and then reversed sharply, which could be indicative that a peak level of car mobility may have been achieved. There are several factors that could explain the recent sharp drop in the growth rate and the significant decline in the total annual vehicle-distance traveled. One has been steadily increasing energy prices, particularly in the first half of 2008 when a third oil shock was unfolding. Yet, as oil prices substantially declined afterwards, there were no resumption of growth. Another is an unfolding recession were lower level of economic activity are directly correlated with lower ridership. The aging of the population may also be a factor at play as well as the slow down in suburbanization. Although it is quite likely that growth rates will resume in the future, they will be much lower and close to zero.