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

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. Further, the proportion of such households increased in 21 of the 30 largest cities, with the 13 cities with the largest proportions showing an increase during that time.

“The proportion of households without a vehicle is likely influenced by a variety of factors,” said Sivak, a research professor at U-M. “Examples of such factors include the quality of public transportation, urban layout and walkability, availability and cost of parking, income and price of fuel.”

According to Sivak, more than half the households in New York City had no vehicle in 2012 (56 percent) and at least a quarter of households in seven other U.S. cities were without a vehicle in 2012: Washington, D.C. (38 percent), Boston (37 percent), Philadelphia (33 percent), San Francisco (31 percent), Baltimore (31 percent), Chicago (28 percent) and Detroit (26 percent).