Gasoline consumption across the U.S. has steadily declined during the last decade. Analysts have chalked up the drop in gas usage over the last ten years to the rise in more efficient technologies, better public transportation, the stalled economy and steadily increasing gas prices.
Imagine, if you will, taking a sheet of paper and cutting it in half. Now take one of those halves and cut it in half again. Now keep repeating the process. As you keep cutting, the difference in the size of the subsequent pieces gets progressively smaller. This simple example is a demonstration of why continuing to increase the fuel mileage of a vehicle has less and less impact once you get beyond about 35-40 mpg.