The correct answer is - 1 million.
Former President Obama's plan about the introduction and usage of plug-in hybrids was that there's should be around 1 million electric vehicles on the roads of the United States in the projected period. Unfortunately, the projection didn't turned out as expected, as it turned out that is was way to optimistic, with the sales of electric vehicles being much lower than initially though it would be.
Instead of 1 million, there were around 280,000 electric vehicles on the roads of the United States in the projected period. It turned out that most of the people still much more prefer the typical vehicles, and are not very fond of changing them with he new technology.