New research by Michael Sivak for the University of Michigan Transportation Research Institute [PDF] indicates that the rate of vehicle ownership by the average American household dropped from a high of 2.07 in 2007 to 1.98 by the end of 2012. This may not sound like much, but when considered in the context of other downward trends in miles driven and fuel consumption, Sivak sees a growing consensus that "motorization in the U.S. might have reached a peak several years ago."
Sivak's research also documents the concurrent rise in the percentage of car-free households in 21 of America's 30 largest cities, notes Angie Schmitt. "Growth in car-free households reflects a number of local factors, including the quality of transit, walkability, and income levels, among other factors, according to Sivak. But he says wider social trends are at work as well."