Analysis of Failures of Solid State Interlocking Systems

 

1. Lack of domain Knowledge in Signalling and Traditional Route Relay interlocking Systems, This creates a technological gap between the software programmers and the Domain consultants. This leads to Errors in software, which might lead to unsafe failures of the system
2. Increasing the complexity of the System by Employing distributed architecture, which is difficult to validate and verify and difficult to maintain, thus leading to very high time repair
3. Extending the working scope of the Interlocking systems  for monitoring and  other non-Interlocking functions, which leads to degraded performance of the system
4. Employing Non-Formal Interlocking principles instead of traditional RRI Principles leads to software complexity. For Ex: The Geographical method needs every system that is installed for new Yard needs validation, which is not practicable.
5. Since the software and hardware is so complex, complete test of the system is not possible and most of the faults are revealed at the field Installation stage or during normal working of the system in field.
6. The software is to be changed for every yard , the software structure should be in a generic form, but we seldom see a generic form and this the stage errors creep in.
7. The lack of standardization in the railway working principles and the core Interlocking principles, the software developers are forced to do changes in the software for every yard in Different railway zones, this is the time that errors in the software creep in.

 

Because of the above said reasons the Interlocking systems have failed to create the necessary confidence in the railway operators. Because of this reason the Solid state Interlocking systems have become unpopular.

 

If we examine broadly the reasons for failure and lack of reliability and maintainability that are forced by the designers are as follows:

 

1. Lack of standardization of interlocking principles, every railway zone has its own set of rules and principles which are conflicting with other railways, this makes the life of the developers difficult because they have change their systems settings and software accordingly.
2. There is no standard book or reference available describing the core interlocking principles, since these rules are only known by the people working in this domain.
3. Increase in the complexity of the software leads to difficulty in testing, since most of the Interlocking systems are sequential machines they are error prone are very difficult to test.

 

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