At Consumer Reports, fuel efficiency has always been an important factor in our vehicle ratings. Helping consumers save money and reducing pollution are also  high priorities. So after years of stagnant and even falling fuel economy, we were encouraged when the federal government this month passed the first increase in fuel economy standards for cars since 1985. The initial Corporate Average Fuel Economy (CAFE) requirements first took effect in 1975.

The new standards require all new passenger vehicles sold in the United States by 2020 to average 35 mpg. That's reported to be about a 40 percent increase over the current standards of 27.5 mpg for cars and 22.2 mpg for pickups, minivans, and SUVs.

However, in our testing, reaching a real-world 35 mpg would require a bigger jump than that. The current new vehicles we have tested have averaged 20.4 mpg overall on our fuel economy test loop—22.8 mpg for cars and just 16.6 mpg for pickups, minivans, and SUVs.

To reach a true 35 mpg in the real world would require an increase of more than 70 percent in overall vehicle efficiency, broken down to more than 50 percent for cars and more than double the efficiency for pickups, minivans, and SUVs combined. That would be a tall order, for sure.

In reality, a 40-percent increase is a more realistic measurement of the new standards than the hyped "35 mpg." The main reason is that the tests automakers must pass to meet Corporate Average Fuel Economy requirements have not been updated since 1985. While fuel economy estimates on new-car window stickers have been updated twice (most recently for the 2008 model year) to bring them closer to reality, the numbers used to compute national averages for regulatory compliance have not. And the new law, set to start raising standards by 2011, doesn't change that. Averages will still be based on the assumption that drivers don't exceed 60 mph on the highway and don't use air conditioning.

A 40-percent improvement would amount to a real-world average of about 28.6 mpg in our testing. Today, a select few diesels, hybrids, and small cars can achieve such high fuel economy. Despite the media hype, by 2020, it still may be only the most fuel-efficient, and possibly revolutionary cars (think plug-in hybrids and fuel-cells) that can deliver more than 35 mpg in the real world—the same place that has the real gas pumps.

—Eric Evarts

Learn more about fuel efficiency and hybrid cars in our Fuel Economy special section.