Nissan will be ready to begin selling multiple models of driverless cars by 2020, it announced on Tuesday. The company has been researching the technology for years in partnership with teams from universities including MIT, Stanford, Oxford, Carnegie Mellon and the University of Tokyo. Work has already begun in Japan, meanwhile, to build a dedicated autonomous driving proving ground -- expected to be completed by the end of fiscal year 2014 -- to test the safety of the vehicles.