A University of Michigan researcher says American households without a vehicle have increased nearly every year since 2007-providing further evidence that motorization may have peaked in the United States.

Following up his research from last year showing that Americans own fewer light-duty vehicles per household, drive them less and consume less fuel than in the past, Michael Sivak of the U-M Transportation Research Institute examined recent trends (2005-12) in the proportion of U.S. households without a car, pickup truck, SUV or minivan.

He also studied variations in this proportion for the 30 largest U.S. cities for 2007 and 2012.

Sivak found that 9.2 percent of U.S. households were without a vehicle in 2012, up from 8.7 percent in 2007.

He also found that the proportion of those households increased in 21 of the 30 largest cities, with the 13 cities with the largest proportions showing an increase during that time.