Just as a side bar:

You do realize that with getting great mileage, the government gets less gas tax revenues and has less money for everything especially road repairs that will increase due to expected increased use. To make up for that short-fall, the government will have to look elsewhere for monies with which to build, maintain and repair roads. I believe 2 states are already looking into a special additional tax system based on miles driven. So, aside from any environmental or international political benefits, you are responsible for the state's budget. What do you do with the following problem.

Last year your state got $1 billion in gas tax revenue and had a $1 billion expenditure for roads. You now anticipate $200 million in gas tax revenues but your roads are expected to cost $1.1 billion for building, maintenance and repairs. Figure out what to do.

Allan