detroit three congressional leaders monday ask top federal environmental safety officials extend 60 days public comment period new vehicle emissions fuel economy standards public advocate need time beyond comment period end sept. 26 absorb 1,000 page draft technical assessment report three say letter environmental safety chiefs week ago u.s. regulators deny similar request extension major automakers u.s. environmental protection agency national highway traffic safety administration say july report automakers technology meet aggressive mandate hike fuel efficiency improvements great obama administration forecast buyers switch pickup truck sport utility vehicles light cars administration first outline goal boost average fleet fuel economy 54.5 miles per gallon regulators forecast 67 percent vehicles sell 2025 would cars since gasoline price fall truck suv sales surge regulators estimate fleet average 50 52.6mpg 2025. letter date monday send epa administrator gina mccarthy national highway traffic safety administration administrator mark rosekind sign three members u.s. house representatives fred upton chairman committee energy commerce ed whitfield chairman subcommittee energy power michael burgess chairman subcommittee commerce manufacture trade congressional leaders ask time study new fuel rule