Evolution of automatic devices in conjunction with signalling on the SNCF

Computerised installations linked to the signalling in French Railways bring computer techniques to signal boxes as operational aids. The first installation, in 1977, was that in the Versailles Chantiers signal box, near Paris. This signal box manages many routes in a complicated area. The second installation, at about the same time, was that involving the traffic management on two 50 km double track sections with sidings and cross-overs. The third installation was at the Paris Invalides signal box, in 1979, on heavily used suburban lines. These three installations used mini computers. But now, with microprocessors and microcomputers, French manufacturers and French Railways (SNCF) have studied new structures with a modular approach. The main differ ence between the systems now being built and the former ones is that it is easier, with the `modules¿, to have decentralised systems, and thus, less development for each installation and a larger facility for building the systems. Moreover, systems managing functions which are not strictly involved in safety in signal boxes have been studied, and fail-safe signalling function design is now in progress. The first French solid-state interlocking signal box put into service has been at Chateauroux.