Formal model for moving block railway interlocking system based on un-directed topology

The safety and complexity of railway interlocking system (RIS) requires the use of advanced methodologies. Formal methods increase quality and provide highest confidence in this area. In this paper, safety analysis of moving block RIS is presented. The system is decomposed into four components, i.e., topology, network state, trains and controls. Formal analysis of the components is presented after further decomposition. Finally, the safety properties preventing collisions and derailing are formalized by integrating with moving blocks of trains under computer based control systems. The railway network is modeled in graph theory. Formal specification is described in VDM-SL and the model is validated using VDM-SL toolbox