U.S. Dept. of Transportation says plan for 54.5 mpg averages by 2025 will be completed 'soon'

The Obama administration plan will require automakers to have a fleet average of 54.5 miles per gallon

The U.S. government said on Wednesday it plans to complete rules "soon" that significantly boost automobile efficiency, despite calls from some Republicans for further evaluation of the regulations.

The Obama administration had planned to finalize standards last week that would require companies to reach an average fuel efficiency across their U.S. fleets of 54.5 miles per gallon by 2025, but the release of the regulations was delayed.

While declining to provide a specific timeline, the Transportation Department stressed the rules are moving forward.

"The rule is still undergoing interagency review and we expect that process to be completed soon," department spokeswoman Lynda Tran said in a statement.

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