A whole lot of exaggerating going on.

If you think the fuel economy of U.S. vehicles is dismal, well, you’re right. Perhaps more right than you know.

Official U.S. EPA statistics ascribe a pathetic average of 20.8 miles per gallon to the 2003 car fleet, about 6 percent lower than 15 years ago. The fleet averaged 22.1 mpg in 1987, before Americans got hooked on gas-guzzling SUVs.

But according to the enviro group Bluewater Network, the actual fuel economy of America’s cars and light trucks is as much as 20 percent lower than the EPA claims.

The Bush administration last week agreed to look into the issue, as a belated response to a petition filed in June 2002 by the group — but cynics can be forgiven for questioning just how hard they’ll look.

Here’s the problem: The EPA’s gas-mileage tests of new vehicle models — conducted in labs rather than on roads — are based on methods and criteria developed 20 years ago and long since obsolete, according to Bluewater Executive Director Russell Long. The result, he says, is that the EPA’s estimates of fuel economy are significantly more optimistic than what most drivers actually experience in the real world.

“The traffic patterns today are totally different than they were two decades ago, and this has serious impacts on a car’s fuel economy,” Long says. For example, ubiquitous urban congestion has resulted in more idling and start-and-stop driving, and average highway driving speeds have increased — all leading to higher fuel consumption. (Get the nitty-gritty on problems with the current testing model in the 2002 Bluewater report “Fuel Economy Falsehoods” [PDF].) Nonetheless, the EPA’s misoverestimated fuel-economy numbers appear on labels affixed to every new car on the sales lot.

“We have a double standard in this country: It’s illegal for corporations to mislead the public about their products. But here the EPA is getting away with what you might call highway robbery — car owners are paying $200 to $300 more every year for gas than the labels indicate they would,” said Long.

The EPA last week opened up a 120-day public-comment period on Bluewater’s request that mileage testing procedures be revamped. (You can submit a comment on the matter yourself if you feel so inclined.) Though it could take months more for the agency to decide what action (if any) to take, Bluewater has applauded this first step.

If the national corporate average fuel economy (CAFE) rules are to be overhauled — as called for by a growing chorus of enviros and politicians, including Democratic presidential candidate John Kerry — it only makes sense that we first consider serious flaws in the program’s underlying infrastructure.

“Clear labeling of fuel efficiency is a prerequisite for everything else,” says Long. “It will steer motorists toward cleaner cars and save them money, not to mention give a clearer picture of the need to reduce our global warming pollution and dependence on foreign oil.”