you first said that we have to decrease our use .... if not by a tax, how should we do it?
Jimmyp5, I think that as you said, it will unfortunately take gas prices to reach $5 per gallon before we begin to pushing automakers into producing medium - high effeciency engines and vehicles. However, I don't think the gov't needs to start collecting even more taxes to do this. That just leads to larger gov't, which I don't like. Even if those tax dollars get thrown to fuel/engine research, it will be wasted, given to only the politricktions friends.
If instead, the gov't would pay a large incentive to the person or company who comes up with, and begins producing high efficiency(70mpg for gasoline vehicles), safe vehicles (the free market has the ability to work outside of the beurocracy of Washington), we will change virtually overnight. Richard Branson has been leading the way with this idea, with his recently announced incentives for just that, but $1 million isn't much incentive to the Big Four.
One other way we could immediately change people's habit's of the autos which they are purchasing, is for the gov't to illiminate the huge tax incentives given to people purchasing vehicles weighing over 6,000lbs. I do think we still need some help for the farmers, but right now, the law is open to anyone owning their own business. In addition to taking away the tax incentive given to the heavy vehicles (which also cause more wear and tear on the roads), increase the tax incentive, given to all people purchasing vehicles which get more than 40 mpg. That incentive should at least equate to the lowest tax incentive currently given to the people purchasing the 6,000lb + vehicles which equates a $25,000 deduction from your income. It can be much more depending on the type of vehicle which you purchase.
Changing the incentives alone, would be enough cause for people to change their purchase habits to buying more effecient vehicles. Add to that, the giving of substantial reward incentive by the gov't, for the person or company bringing to the market, high effeciency vehicles, and I think we can do wonders to change our purchasing habits, without getting the gov't more tied into the red tape with Big Auto and Big Oil, and it can be done in the private sector, rather than creating more gov't.