A report from the Earth Policy Institute suggests that the size of the US car fleet has apparently peaked and is now in decline.  In 2009, cars scrapped (14m) exceeded the new cars sold (10m) for the first time since World War II.  Although generally attributed to the recession, the report suggests that this shrinkage could continue on account of a number of trends - market saturation, ongoing urbanization, economic uncertainty, oil insecurity, rising gasoline prices, frustration with traffic congestion, mounting concerns about climate change, and a declining interest in cars among young people.

The report argues that market saturation may be the dominant contributor to the peaking of the US fleet, with 246 million registered motor vehicles and 209 million licensed drivers—nearly 5 vehicles for every 4 drivers. Japan may offer some clues to the US future. Both more densely populated and highly urbanized than the United States, Japan apparently reached car saturation in 1990. Since then its annual car sales have shrunk by 21 percent.

Of course, what matters for carbon emissions and congestion is how much use is made of the car fleet.  Scrapping little used cars may not have much impact.  However, a 2008 report from the Brookings Institution observed that per capita driving (vehicle miles travelled) in the US has shown flat-lining after 2000 and falling rates since 2005.  So there is evidence to support the interesting and helpful possibility that car ownership and use in the US may have peaked.