The ELEKTRA railway signalling system: field experience with an actively replicated system with diversity

Since the beginning of the century, Alcatel Austria has been the main supplier of railway signalling products in Austria. In 1985, Alcatel Austria began developing the electronic interlocking system ELEKTRA. In order to meet the stringent safety requirements for railway interlocking applications, a two channel system based on design diversity has been developed. High availability and reliability are achieved by using actively triplicated redundancy with on-line recovery. In 1989, the first system was put into operation. About 15 railway interlocking systems are in operation and further installations are ongoing. The paper presents the fault tolerance mechanisms used for design faults as well as physical faults. The experience gained with these concepts is also discussed.<>