Submitted: May 22, 2008 - From the mid-1970s to 1990, the average fuel economy for all vehicles on the road in the U.S. doubled from about 14 to 28 miles per gallon (mpg). By 2005, it had dropped to 24 mpg. Driving a fuel-efficient vehicle will save you money on gas, of course, but such a decision has other, broader, effects.

Nature required more than 200 million years to develop all of the oil below the earth's…