In spite of the fact that the US Environmental Protection Agency
generates and publishes fuel economy
ratings for US market cars and trucks, they aren't responsible for the regulations. The measurement of fuel economy ratings actually came about as a by-product of the emissions testing that the EPA
has been responsible for since the original Clean Air Act. However, as various factions in Congress bicker over how much to increase fuel economy requirements and over what time frame, the EPA is finally moving ahead with creating rules on greenhouse gas emissions.
By establishing limits on carbon dioxide emissions, they will for the first time be effectively limiting fuel consumption. The EPA is pulling together officials from a variety of agencies to draft the new regulations in accordance with President Bush's mandate earlier this year as well as the Supreme Court ruling that they have the authority to regulate greenhouse gases. Meanwhile congress will be back in session next week and expects to take up CAFE again.
[Source: Automotive News - Sub. req'd]