Author(s)

B. Dehbonei & F. Mejia

Abstract

Formal development of software in railways safety critical systems B. Dehbonei & F. Mejia GEC-ALSTHOM, 33, rue des Bateliers, 93400, Saint-Ouen, France 1 Introduction Software is increasingly involved in the new generation of railways signalling systems. In systems such as interlocking, train routing devices or automatic train protection, electronic or electromechanical devices that previously pro- vided safety critical functions are being replaced by computers. While safety procedures for developing critical electronic and electromechanical systems are fully mastered, no similar procedures are available for computerized modules. SACEM was the first french railways signalling system where software played a major role in safety critical functions. SACEM is an automatic train protection used in the Paris RER line A. Its purpose is to allow the train interstation interval to be decreased from 2.5 minutes down to 2 minutes without lose of passegers safety. The validation phase of

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