Interlocking Control by Distributed Signal Boxes: Design and Verification with the SPIN Model Checker

Control systems are required to comply with certain safety and liveness correctness properties. In most cases, such systems have an intrinsic degree of complexity and it is not easy to formally analyze them, due to the resulting large state space. Also, exhaustive simulation and testing can easily miss system errors, whether they are life-critical or not. In this work, we introduce an interlocking control approach that is based on the use of the so-called

Distributed Signal Boxes (DSBs)

. The proposed control design is applied to a railway-interlocking problem and more precisely, to the Athens underground metro system. Signal boxes correspond to the network’s interlocking points and communicate only with their neighbor signal boxes. Communication takes place by the use of rendezvous communication channels. This design results in a simple interlocking control approach that compared to other centralized solutions produces a smaller and easier to analyze state space. Formal analysis and verification is performed with the SPIN model checker.