Any of these are short term solutions in my opinion. We need to remove our reliance from the internal combustion engine. No matter WHAT fuel you are burning it still pollutes...and 100's of millions of vehicles is just too much pollution. When solar takes over, then we can have electric cars that don't just move the pollution from the tailpipe to the electricity generating location. (Although that argument doesn't have teeth as much as naysayers of current electrics would have you believe).