The Bush administration says it won't finish new vehicle fuel-efficiency rules, leaving the issue to the incoming Obama administration.
The Transportation Department said Wednesday the recent financial problems of automakers will require the next administration "to conduct a thorough review of matters affecting the industry."
In April, the current administration said the next generation of new cars and trucks should be required to meet a fleet average of 31.6 miles per gallon by 2015. The proposal was part of a new energy law that requires new cars and trucks to meet 35 mpg by 2020, a 40 percent increase.
The regulations would cost the companies tens of billions of dollars at a time when General Motors Corp. and Chrysler LLC are struggling to survive and have received a federal bailout.