In order to introduce autonomous driving systems into the market, socially acceptable and technically sound safety assurance methodologies need to be agreed. In Japan, vehicle manufacturers and traffic safety experts have gathered regularly under the auspice of the Ministry of Economy, Trade and Industry, in a coordinated initiative to harmonize the required collaborative research, methodology development and standardization activities. Within this initiative, a comprehensive safety assurance process is to be agreed and made publicly available. The process shall be driven by top safety goals defined by authorities, shall consider the systems’ performance limitations, and must be supported by state-of-the-art methodologies and real-world data. At this point, consensus on the overall safety assurance process for SAE Level 3+ autonomy in motorways as well as on the methodology to develop testing scenarios has been achieved and the results are hereby reported. The process and methodology are directly applicable to support the development of systems towards a safer autonomous driving society.