There are 230 million vehicles in the U.S. fleet, and it turns over every 15 years. If the most extreme CAFE rules were implemented immediately, it would likely be a decade before they made a meaningful dent in U.S. fuel consumption.

Hear Ward's AutoWorld Editor Drew Winter's latest take on the auto industry in his weekly report on Detroit's WJR radio:

Boosting CAFE Slow Way to Reduce Fuel Consumption