To answer this, we must turn the telescope around and look at gasoline from the global perspective.
Motor vehicles use about a third of all petroleum. The other two-thirds is used in industry, agriculture, construction, the petro-chemical industry, heating and other forms of transportation. Motor vehicles, in turn, account for only about 14 percent of all fossil fuel use.
Doubling fuel efficiency, say from 20 mpg to 40 mpg, would appear to reduce gasoline use by 50 percent and fossil fuel use by 7 percent. Sounds good, except that energy does not hold still while we try to fix it.
It would take some 15 to 20 years for the world’s motor vehicle fleet to reach 40 mpg average. During this time the number of vehicle will have nearly doubled leaving us with very little net savings. Also the other uses of petroleum (non-motor vehicles) and fossil fuel consumption would continue to grow regardless of improvements in fuel economy.
The result would be the continued increase, albeit at a slightly reduced rate, of oil and fossil fuel consumption over the next 15 to 20 years (Section 9, Example 5, The Global Energy Handbook).
