The Center for Automotive Research (CAR) contends that as fuel efficiency rises to very high levels, the benefit to the customer shrinks. At $5 per gallon, for example, a 15,000-mile-a-year driver can save $3,750 on gasoline annually by jumping from 10mpg to 20mpg. But by going from 40mpg to 50mpg, the savings drop to only $375 annually, the curve shows. As consumers reach those limits, CAR says they are likely to keep their current vehicles longer, a phenomenon it refers to as the "Cuban-ization" of the American auto market.
(Source: Center for Automotive Research)