11．Method to verify system specifications based on safety requirements in structured format for train control systems

When developing IT based train control systems, the safety of their technical specifications must be checked by railways signaling experts etc. Train control systems are made up of functions for speed checking and setting movement authorities, inter alia. The process for checking the specifications for the overall system and each of its functions is very time consuming and labor intensive. A proposal was therefore made to make this procedure more efficient while guaranteeing the level of safety achieved through this method (Fig.1).

The special feature of this format is that it takes into account the order in which safety measures should be applied to meet the system’s safety requirements, and also distinguishes between inherent safety measures and additional ones.

Inherent safety measures such as hard ware architecture and control logic for fundamental removal of internal system hazard sources are listed in an inherent safety measure column.

Based on this format, the system designers themselves can identify from the design specifications the safety requirements in the system and at the same time verify that the safety measures have been met.

Furthermore, the format of safety requirements can be used as a method for checking the overall safety of the system as it can serve to verify the correct contents of the design specifications themselves and compatibility with the design specifications of the other constitutive functions (Fig.2).