Solid-state interlocking (SSI): an integrated electronic signalling system for mainline railways

For a number of years, British Rail (BR) has been working towards an electronic replacement for the electromechanical interlockings which are at the heart of railway signalling systems. This work has led to the successful development of the BR solid-state interlocking, an all-electronic signalling system for mainline application which has been in operation at Leamington Spa, Warks., UK, since September 1985. The paper describes the problems confronting railway administrations wishing to exploit new technology and discusses some of the options available to the designer of safety-critical systems. The solid-state interlocking is described, with particular emphasis on the techniques used to ensure safety and reliability, its software and data structures, and the methods used to communicate with trackside equipment. The specially developed scheme design language is illustrated and details are given of support facilities such as data compilers and simulation equipment. The salient features of the Leamington Spa pilot scheme are described.