District Court in Vermont on Wednesday upheld a state law that calls for a 30 percent reduction in the amount of carbon dioxide, a greenhouse gas, emitted by cars and certain light trucks. In his decision, Judge William K. Sessions found that the Vermont law -- which regulates greenhouse gas emissions -- did not conflict with federal regulations on fuel economy. "The plaintiffs failed to prove the regulations were preempted," Sessions wrote in his decision.

Automakers General Motors Corp. and DaimlerChrysler AG -- which has since sold its Chrysler unit -- sued in 2005 to block the law, arguing that states do not have the authority to regulate the amount of CO2 released by cars, which is closely related to fuel economy.

Vermont is one of nearly a dozen states that followed California's lead in adopting the strict standard, which is tougher than federal rules and is intended to reduce the rise in global temperatures and changing weather patterns associated with greenhouse gas emissions.

The automakers argued that they could not meet the new standards, and in court testimony said they would have to pull out of the state as a result.