Every year millions of new cars are put on the road and millions of old cars end up in the scrap heap. Its the cycle of life... for a car. The BTS National Transportation Statistics has a ton of data. Table 4-58 in the report gives the number of vehicles scrapped in the US. The entire report is available in a single 500+ page PDF.
Here's the data in graph form :
Notice that between the year 2000 and the year 2005 the total # of vehicles scrapped actually went down quite significantly. I'm not sure why that is. I would assume there is a relationship between the economic cycles and the number of cars scrapped. Seems to me that people would scrap more cars when the economy is booming as that is when they're more likely to go get a new car. Maybe thats the trend we're seeing in the charts for the 2000 to 2009 periods.