I'll try to stay out of the politics, but WILLY is right - this conversation will almost inevitably head in that direction at some point.
There are already plenty of non-gasoline vehicles on the road today - diesel, ethanol, electric, hybrid, WVO (waste vegetable oil), SVO (straight vegetable oil). Solar and hydrogen are even possible alternatives in the near future. The problem is that most of them aren't profitable, and have to compete with gasoline which is still relatively inexpensive. The other problem is a supply and demand issue - there is tons of petroleum being pumped out of the ground as we speak, and it breaks down into several different fuels in fixed proportions (kerosene, diesel, gasoline, jet fuel, etc). Unless you eliminate all forms of petroleum based energy, you still have to find something to do with all the byproducts. Most of the developed world is so dependant on these products, only a gradual transition is possible - it will likely come in the forms of biodiesel, ethanol, and hybrids. Will this move us closer to hydrogen or electric powered vehicles? Yes, but it won't happen overnight.
I think most people who fully understand the energy problems will tell you that we will inevitably have to stop using petroleum based products not only because of pollution (the global warming debate), but because it's in limited supply. If we start transitioning to alternative fuels, the supply could last much longer, but it will run out one day if we continue pumping.
My predictions (or let's call them wild guesses ):
-- Majority alternative fuels: 20-30 years
-- Completely off petroluem: not in my lifetime
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