Formalizing and Analyzing System Requirements of Automatic Train Operation over ETCS Using Event-B

Abstract

The European Railway Traffic Management System (ERTMS) aims at the replacement of incompatible national railway traffic management systems in Europe. A part of ERTMS is the European Train Control System (ETCS). ETCS is an automatic train protection system and can collaborate with an automatic train operation system (ATO). ATO can control and monitor the braking, traction and door system of a train. This collaboration is called ATO over ETCS. In this paper we describe the experiences gained in the formalization and the formal analysis of system requirements related to the modes of the ATO onboard unit and its interfaces to train, ATO trackside unit, and ETCS onboard unit. A primary goal to achieve was the stepwise and systematic construction of an Event-B specification tightly coupled with the requirements based on a bidirectional traceability concept. Another goal was the formal verification of important safety properties related to the mode transitions and transition conditions of the ATO onboard unit.