ITC Report 1 Safety System Validation

with regard to the cross-acceptance of signalling systems by the railways


The Institution of Railway Signal Engineers decided in 1990 to establish a Technical Committee to represent the Institution’s members and to further the advance of railway signalling techniques. 

The committee comprised senior engineers from the railway administrations and railway contractors of Europe. 

The committee identified that a primary concern of all Signal Engineers was the difficulty and cost of introducing new technology into signalling systems, and that a large proportion of this cost stemmed from the need to provide a proof of safety for each system. 

As the proof was currently required in a different format and frequently to different standards for virtually every application it was considered that a great deal of effort was being wasted and that as a result the cost of the systems was higher than it should be. More importantly it was considered that the adoption of common standards would enable the resources applied to the proof of safety to be coordinated and hence should result in higher standards being obtained. 

This first report covers the acceptance of safety signalling systems and recommends a common standard of acceptance. The committee have produced their report in the knowledge of the many other such committees that have been established in related disciplines working on similar problems stemming from the introduction of new technology and the application of the latest safety analysis techniques. 

Wherever possible the work of these committees has been incorporated in the report, and one of the primary aims of the report is to influence the work of the current committees by providing a vehicle for the views of the Railway Signalling Profession to be expressed. 

A number of basic essentials for a signalling safety system are established: 

‐ That total system safety must be considered. (This must cover the safety of passengers at all stages including the safety of the railway itself throughout the duration of signalling equipment failures where emergency procedures have to be introduced) 

‐ That the function of the particular part of the signalling system considered must define the level of safety required

‐ That safety is only achieved if the total life cycle of the equipment is considered

‐ That minimum standards must be established for each level of safety required

‐ That safety can only be assured through the strict management of all the processes involved in specification, production, testing, maintenance, and operation of the signalling system.

Although a number of standards exist none currently cover all of the above requirements. The draft standards “Software for Computers in the Application of Safety‐Related Systems” (IEC 65A, WG9) and “Functional Safety of Programmable Electronic Systems: Generic Aspects” (IEC 65A, WG10) cover the procedural requirements for safety systems and the committee considers that these form an excellent base for their recommendations.

Based on the IEC standards the Committee has concluded that Railway Signalling Systems require a degree of safety according to the following categories:

Degree 4 ‐ to prevent train collision and derailment

Degree 3 ‐ to identify integrity and characteristics of train

Degree 2 ‐ to manage rail traffic

Degree 1 ‐ to inform passenger

Degree 0 ‐ to manage the railway

The committee have made recommendations for each safety degree required, so that a common standard can be adopted for the acceptance of systems. Provided systems are produced and accepted against these recommendations and provided the documentation of the processes of production and acceptance are sufficiently thorough it is the belief of the committee that cross acceptance of systems can be achieved.

It is the intention of the Institution to offer its contribution to the European Railway Community in the railway signalling field in cooperation with existing organisations. It could be a joined contribution to some specific and urgent topics with the possibility of very specialised studies with financial support by the European Community, if necessary.

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