When you run the numbers, you will find that there is no way to produce enough ethanol to replace fosil fuels. Look at what is happening now. The price of milk is already going up because corn that would normally feed cows is going to making ethanol, so that raises the price of cow feed. Farmers are plowing under apple orchards and agave farms to grow corn, which raises the price of apples and taquilla:holysheep: .
This is happening with less than 1 percent of the auto fuel coming from ethanol. Imagine what would happen when if it were 100%.
Fuel Cells would work, except that to make the hydrogen that you need for the Fuel Cells, it takes energy. In fact, it takes more energy to make hydrogen than you can get out of it when you burn it.
Electricity-run vehicles are really the only way. The problem with that is around 70% of the electricty (in the USA) is generated using coal and natural gas,both fossil fuels that create smog and green house gasses.
Solar Energy: To replace the coal/Natural Gas, you would need to cover over half the land mass of the U.S. with solar panels.
Wind: Well, you need areas that have a constant (or near constant) wind and I remember reading that 80% of them already have wind generators so there isn't much room to grow.
Nuclear Energy: The only answer!:smoke1: