Developing CBTC system safety requirement hierarchy through STPA methodology.

Area of Science:

• Engineering
• Computer Science
• Systems Safety

Background:

• Safety-critical systems like railway signaling face high costs from failures.
• Modern systems, including Communication-Based Train Control (CBTC), introduce new accident types due to software and complex interactions.
• Traditional hazard analysis methods are inadequate for these advanced systems.

Purpose of the Study:

• To develop an improved methodology for safety requirement generation in modern safety-critical systems.
• To address the limitations of traditional hazard analysis in the context of CBTC systems.
• To enhance risk management and hazard analysis for railway signaling.

Main Methods:

• Utilized Systems-Theoretic Process Analysis (STPA) as a core hazard analysis technique.
• Developed a hierarchical approach integrating STPA with hierarchical modeling.
• Established traceability from safety requirements to system architectures and allocated requirements to subsystems.

Main Results:

• The methodology effectively links safety requirements to specific architectures.
• System-level safety requirements were refined and allocated to relevant subsystems.
• Abstracted safety requirements at higher levels facilitate easier lower-level implementation changes.

Conclusions:

• The combined hierarchical and STPA approach enhances safety requirement development for CBTC systems.
• This methodology provides early insights into potential hazards and improves risk management.
• It facilitates the generation of accurate and complete safety requirements for complex systems.