New horizons for train location and signalling
Despite the many great advancements that have taken place in railway signalling systems, some concerns still exist – notably regarding SIL 4 (Safety Integrity Level) train locationing. Giuseppe Fazio, Mauro Giaconi, Salvatore Vetruccio, Matteo Telesca and Alessandro Giuliani from the Italian rail community highlight the main issues related to current systems alongside some proposed solutions that are under consideration by the academic community.
These relate to track circuits that consist of galvanically isolated rail links. In this context, circulating currents in rails are frequently coded in order to communicate with trains semaphore states (Coded Current Automatic Block – BACC). The issues related to the presence of such joints include the following:
- The joints set limits to train speeds
- They represent single points of failure with resulting maintenance issues
- They are intrinsically difficult to check their own integrity and that of the overall rail
- Above all, their replacement with more sophisticated systems involves the issue of non-compatibility with present in-vehicle systems. Sometimes on updating rail links – despite being a huge additional cost – it is preferable to sacrifice compatibility with present in-vehicle systems for signal continuous repetition through coded currents. The priority is to remove fragile insulated joints.
Usually used track circuits without insulated joints are axle counters and audio frequency track circuits. The main issues encountered with such circuits are as follows: