The tremendous growth in the transportation sector in China may make the number of vehicles produced in this country eclipse the number of vehicles produced in the United States this year. The United States has been at or near the top of the automobile manufacturing sector worldwide since the invention of the automobile.
In 2007, Japan produced 11,596,000 vehicles, with 10,781,000 from the United States and 8,882,000 vehicles from China. China is predicted to produce more than 10 million vehicles this year, and the United States is predicted to produce less than 10 million.
There’s a good Wikipedia entry on vehicle manufacturing by country, with metrics on manufacturer volumes and relationships.