A scenario-based safety argumentation for CBTC safety case architecture

Abstract

The Communication based Train Control System (CBTC), as a symbol that China has stepped into the stage of rapid urban rail traffic development, is a safety-critical system that guarantees rail traffic safe-operating and high transportation efficiency. The safety case for the CBTC generic product is an essential justification document to prove the system can be accepted as adequately safe. To extract safety requirements implicitly illuminated within the system requirement specification, operational scenarios are widely used to depict the behaviours and interactions of subsystems and components, which becomes a challenge when constructing safety case architecture from the aspect of system function. This paper presents a promising method based on Goal Structuring Notation (GSN) to establish a composition of safety argumentations for managing safety cases. The method introduces the concept of safety argument modules to express rationally encapsulated goal-based safety claim sets that conform to safety requirements, but are deduced in accordance with hazard analysis based on the operational scenarios. An example generic modular safety case architecture for CBTC generic products is presented to illustrate how the whole safety case architecture is structured to be in line with system requirements, and the ease with which module updates and reuse, according to revises for system development, can be performed. © 2010 WIT Press.