In April, Peters presented the department's plan to increase the fuel efficiency requirement for U.S. vehicles to 31.6 miles per gallon in the next seven years, The Detroit News reported Saturday.

It is reported the plan would require a 4.5 percent yearly growth, a speedier rate than indicated by Congress when it asked for a revamp of passenger car fuel efficiency regulations in December.

Peters Friday called attention to the fact that the initial plan estimated gas prices would be about $2.26 a gallon in 2015, increasing to $2.51 in the next 15 years.

"As we look toward the finalization of the rule and look again what the average fuel costs are then, I think we're going to make more progress on the miles per gallon at a lower overall cost," Peters said.