Cars and trucks averaging 62 miles per gallon? Seems extraordinary now, but ... automakers could be required to build lineups like that by 2025, making today's high-mileage hybrids seem conventional and turning gas guzzlers into mere relics. By a decade and a half from now, in 2025, a carmaker's fleet of new vehicles may need to meet a standard somewhere from 47 mpg to 62 mpg, the Transportation Department and Environmental Protection Agency said. Those mileage gains that would be the equivalent of an annual decrease in carbon dioxide emissions per mile of 3 to 6 percent. The government envisions gas-electric hybrids making up about half the lineup of new vehicles under the most aggressive standards, while electrics and plug-ins would comprise about 10 percent of the fleet. After little progress during the past three decades, rules adopted earlier this year will lift the new vehicle fleet average to 35.5 mpg by 2016, an increase of more than 40 percent over current standards.Fuel efficiency standards are designed to improve gas mileage across each automaker's lineup and across the nation's entire fleet of new vehicles. Vehicles must meet differing standards based on their dimensions. Compact cars must get better mileage than sport utility vehicles, for example, but requirements for all types of vehicles will go up.