Sorry that I have to correct but due to lower energy content 7.5 billion gallons of ethanol are equivelent to just 4.6 billion gallons of gasoline or 109 mln.barrels of oil.
This would save 5 days (1.37%) of current USA oil consumption annually which might not be impressive but is not that insignificant. I agree though that with higher CAFE we could save much more.
Thanks for the figures.  I wonder if biodiesel is similarly energetically challanged.