Annual U.S. Motor Vehicle Production
1. I think that mostly the automakers are interested in this statistic because they have to know how big the demand will be in the next year/quarter/month. But also suppliers might be interested as well as the government, because it has to care for a well equipped infrastructure (highways, parking spots, intelligent traffic systems).
2. OICA, the “International Organization of Motor Vehicle Manufacturers” publishes that statistic every year. But probably there are several other statistics about monthly production and different other variations. I assume that the number are the added numbers of all the vehicle assembly plants within the U.S. .
3. Due to the freshly started year 2011 the numbers for 2010 are not published yet. That is why I only can write down the number for 2009: in 2009 there were 5,708,852 vehicles produced in the US. But, what I do can say is that the estimate number for 2010 is about 7,800,000 vehicles, that is an increase of 36,6 % and therefore pretty considerable. You also can figure out with these datas that the U.S. in 2009 has been the third biggest vehicle producer throughout the world. First one is China with 13,790,994 vehicles, followed by Japan with 7,934,516 vehicles.
International Organization of Motor Vehicle Manufacturers, 2009 production statistics, 2009, http://www.thetruthaboutcars.com/2010/12/car-production-2010-u-s-a-beats-china-in-percentages/