Formal Safety Analysis in Transportation Control

Transportation control systems are safety critical systems. While a couple of years ago control systems mainly used to be built up from (electro-) mechanical devices, nowadays more and more functionality is software controlled. To sustain the high level safety standards for these embedded systems, we propose to use fault tree analysis integrated with formal methods for analyzing system safety. This approach combines typical safety analysis techniques from engineering resp. software engineering. Fault tree analysis mainly focuses on system safety and considers defective components whereas formal methods mainly focuses on functional correctness. This paper presents the methodical aspects of the combination. To benefit from both, it is important to retain the different points of view of fault tree analysis and formal methods and nevertheless end up with an integrated formal model, where safety properties can formally be proven.