Railway companies operating in major cities or between major cities must conduct high-density transportation and safely transport as many passengers as possible. Securing transportation capacity and high degrees of safety and reliability are required for train control systems in high-density train operation sections. Of the many lines operated by JR East, the Shinkansen and Tokyo Metropolitan Area line sections are sections with very strong needs concerning high-density, safe, and stable transportation. We have proposed an autonomous decentralized train control system as a system that meets these requirements and construction of this new system is currently proceeding. However, replacement by the new system while operating the current ATC system must not influence daily operations of the latter. In addition, it is also necessary to configure the new system so that technology that allows the current and new systems to coexist, including system starting and countermeasures in emergencies, etc. does not influence the overall system. The technology that supports this is assurance technologies. This technology has also been used in the train control system for the Yamanote and Keihin Tohoku Lines. The following is a report on assurance technologies.