DETROIT—The Obama administration on Thursday proposed a 10-year, $4 billion push to encourage the development of self-driving cars, hoping to one day eliminate roadway deaths altogether. The U.S. Department of Transportation’s National Highway Traffic Safety Administration regulators said they would seek unified national regulations on self-driving cars. They will also encourage automakers to claim an exemption to safety standards allowing companies to test new technology on a fleet of up to 2,500 vehicles for up to two years.…