U.S. cars and light trucks will become more fuel efficient and safer — but also more expensive — by the end of the next decade, as a result of increasingly stringent environmental standards, a new research report said on Thursday. The report, released by the National Research Council, said fuel economy and greenhouse gas emission standards will drive new powertrain designs, alternative fuels, more advanced materials and changes to body vehicle design. Most gains in fuel consumption will come from improvements to gasoline internal combustion engines, which are expected to dominate automotives through 2025, according to the report, which was sponsored by the National Highway Traffic Safety Administration.