OK - I've done a bunch of work on this; unfortunately my RSI is acting up again, and I can't give the amount of response that it deserves. The short version is that gas tax is not best solution. Yeah we not only drive inefficient cars, but we drive them too far. But for the most part that is not a choice. We live further from work and that is not something that will change in the short run. You want to cut US energy consumption feebates (gas guzzler taxes/efficient car subsidies), regulation and infrastructure investement will give you better results. Incidentally switching from car to buses is not much of a solution. Buses in cities, suburbs and rural areas have passenger miles per gallon comparable to cars, by many measure worse. The only case where buses get better mileage than cars is on really long trips - basically Greyhound and such. Buses are often the only means of travel available for people who don't have cars. But they are not energy savers. Check out the standard DOT statistics on this. You want to get people out of their cars you are going to have provide transit. Very few places have much of a light rail structure in place. Manhattans subway system, and Oregons light rail are exceptions not the rule. Most people don't have rail transit available.
Once I've had my cortisone shot, I'll post further. This is the first time I've checked my email in five days and I could not resist posting on the subject, cauase you usually get these things right, and I wanted to provide a hint that you are on the wrong path. We have structural things in place that Sweden does not. Ten dollar a gallon gas will save energy in the short run mainly by hurting poor and working people. Compensating subsidies would mostly go right back into gas consumption. Write the gas guzzler tax large - that is in general put a tax on energy consuming capital goods and use to revenues to provide subsisides to energy saving goods and renewable source. Put in place massive public spending on efficiency and renewable infrastrure. Five or ten years into that transition, a gas tax will make sense because there will actually be infrastructure so that people can respond to higher prices in some way other than suffering.
Europe never dismantled their rail structure; so high gas taxes occured in a context where people had reasonable alternatives. Even so infrastrucure neglect on the part of many European nations has led to a shift from transit to the automobile - in the sense that auto miles in ratio to transit miles are increasing. Gas taxes only make sense when people have an alternative.
Short version of a workable energy program for America:
1) Apollo Alliance multiple by five minus "clean coal" portion 2)Feebates - taxes on energy consuming capital goods revenue from which subsidizes energys saving capital goods 3)Efficiency regulations - modeled on best of breed Japanese reg being challenge by WTO 4) Energy taxes only after this has been in place five or ten years,
Not saying energy taxes before that will have no effect - but that the program I've outline above will give you much better results for the investment. Look at the feebates as a form of energy tax. You will get much more response to the price being charged at the time of capital investment - which is the key decision in energy efficiency than at the time of consumption when capital infrastructure is already in place.