text: Now we finally reach the United States after hearing about Germany, Paris, and Paris in terms of trying to limit the use of cars. Michael Sivak, who studies the trend of car usgae in America and is a reasearch professor at the University of Michigan's Transportation Research Institute, reports:"What most intrigues me is that rates of car ownership per household and per person started to come down to two to three years before the downturn, I think that means something more fundamental is going on." Mr. Sivak's research has found demogaphic shifts in the driving populations that suggest that the trend may accelerate. There has been a large drop in the percentage of 16-39-year-olds getting a license, while older people are likely to retain their license at they age. A study last year has also found that driving by young people decresaed 23 percent between 2001 and 2009.