The Obama administration has finalized new fuel economy rules that will require the fleet-wide average of new cars and trucks sold in the U.S. to double over the next 13 years. The average fuel economy must reach 54.5 miles per gallon by 2025, up from 28.6 mpg at the end of last year. The regulations will bring dramatic changes to the cars and trucks in U.S. showrooms, with the goal of cutting greenhouse gas emissions and fuel consumption. To meet the standard, automakers will need to introduce new technology to improve gasoline-powered engines. The administration says the latest changes will save families more than $1.7 trillion in fuel costs and bring an average savings of $8,000 over the lifetime of a new vehicle sold in 2025. The standards also are the biggest step the U.S. government has ever taken toward cutting greenhouse gas emissions. The gas mileage requirements will be phased in gradually and get tougher starting in 2017. They build on a 2009 deal between the Obama administration and automakers that committed cars and trucks to average 35.5 mpg by model year 2016. The requirements, which can be imposed without congressional approval, will be reviewed in 2018 and could be reduced if the technology isn’t available to meet the standards. The rules are tough, but General Motors, the largest U.S. car company, will roll out features to comply, spokesman Greg Martin said. “Consumers want higher fuel efficiency in their cars and trucks, and GM is going to give it to them,” he said. The administration likes to tout cooperation between automakers and the government in forming the latest rules.