Here's the simple arithmetic behind the gasoline tax. Gasoline sells, at this time, for a little under $4 a gallon. Most of us have autos that get 30 mpg. In the future we will be able to purchase autos that deliver 40 mpg, or those electric cars that don't use gasoline at all. We will have the same number of autos, at least, on our highways in five years as we do today. Our receipts from the current level of taxation will be down by 30 percent or more because the new autos will consume two-thirds the amount of gasoline. The electric cars add an additional spiral to the reduction.