The EPA has reevaluated its formula to compute fuel economy ratings and have introduced a stricter mpg formula for 2008 models. The revision will result in a predicted 8-percent to 12-percent drop in mpg ratios for most vehicles, and a 30-percent drop for hybrids, writes Automotive News.These new numbers, however, do not mean that the new vehicles burn any more fuel than the old ones; they just reflect the new formula's more accurate miles-to-gallon ratio.At the urging of an environmental group, the EPA reworked its formula to better reflect today's driving, allowing for more stop-and-go driving, faster acceleration and higher freeway speeds. Under these new criteria, numbers have fallen by as much three mpg for both city and highway driving as compared to the EPA's previous formula. But this revision does not affect automaker's targets under corporate average fuel economy regulations. Those figures, generated by the National Highway Traffic Safety Administration from automakers' tests, are the starting point for the EPA calculations. The new numbers will be used for 2008 vehicles. This miles-per-gallon revision is the first in 20 years and the biggest in 30 years of government ratings for fuel economy.