201703 – Gillespie – Are CAD Drawings the Best Way to Design Signalling Systems?

Currently most, if not all, railway signalling design around the world is done using multi-purpose Computer Aided Design (CAD) software applications. This approach has evolved from the hand drawn circuit wiring diagrams that were used for relay based interlocking. CAD applications are employed to create drawing packs comprised of multiple, independent, formatted sheets describing the wiring and other related information. The manual process to create this detailed package often results in a mismatch between information on different drawings, wasting time and incurring additional costs. This methodology also depends on a very thorough, time-consuming, manual verification of every element of every drawing once they are all completed.

This paper explores a viable alternative to CAD for designing modern railway signalling systems. SIM (System Information Modelling) has been used successfully for the design of many complex power, control, IT and communications systems on projects around the world over the last 15 – 20 years.

A System Information Model is a 1:1 representation of the real system. The SIM contains generic libraries of objects. Any information known about generic objects is captured as a data attribute or attached as a file. Designers define what equipment is required, where the equipment is to be located and how it is to be connected. There is no requirement to separately document terminals, contacts, cable core lists etc. as this information can all be extracted directly from the model, significantly improving accuracy, while cutting costs.

Modern railway signalling systems now incorporate computer-based interlocking, and the wiring is predominantly simple input/output functions, so, is CAD really the best way to design these high integrity systems?