How many cars?

United States: 800 cars for 1000 inhabitants
European Union: 600 cars for 1000 inhabitants (2006 data)
56% of motorised families have 1 car, 37% have 2 cars, 7% have 3 cars and more.
18% of families in town don’t have a car and less than 10% in countryside.
(source:Mobilités urbaines, Jean-pierre Orfeuil, 2008.)

Since the 90’s we observe a world generalization of individual cars. In China like in India there are 15 cars for 1000 inhabitants but this motorisation rate has grown far more quickly than in other countries between 1990 and 2003 and it will probably grow faster, especially because those countries are the most populated in the world. While Car industry, in developed countries, is at the moment in serious difficulties, China car purchase has been increased by 5%; on million of cars have been sold in March 2009. (Le Courier International, nº964, Avril 2009) This growth is related to the reduction of taxes on car purchase, which is part of the government economic plan.
What can be the consequences if those countries will reach the same amount of car than U.S. or Europe?