To eliminate the main cause of the emergency braking of the metro, at least 60 of those that took place between March and October 2019, it was enough to reduce the braking force when the trains of the “red” are approaching the stops. Here is what happened: the M1 trains move in automatic gear, controlled not by the driver, but by the central system, which makes them move while always keeping the position of all the trains under control. In approach to the docks, the system was programmed with a too marked slowing force, so sometimes the wheels “skated” on the tracks. Nothing dangerous, or that the passengers have ever noticed: the skidding usually took place at 5 kilometers per hour, but that anomaly made the “localization” disappear, that is, the central brain “lost” the train, and then went into a state of alert, triggering the train behind the maximum power block: for a danger that, in reality, was not there. On March 15, 2020 Alstom, after the analyzes led by the experts of the Public Prosecutor’s Office, reduces the “braking effort” at the docks, then gradually adapts the software on the vehicles (at which Covid-19 has already spread) and from March 31st there were no more emergency braking caused by skidding.
The French company Alstom
The countermeasure appears simple (even if on a technical level it is not), but it is emblematic of a work of analysis, updating and solution of the problems that the French multinational of signaling systems should have done (as requested several times by Atm, according to deeds in the hands of the Prosecutor’s Office) and which he had never carried out before the investigation was opened. Also because at the time Atm had identified “skidding” as a possible cause of the blocks, but (not knowing the system problem) he continued to do maintenance by “grinding” the tracks, without this leading to an improvement.
The experts of the Public Prosecutor’s Office
The two experts appointed by the Public Prosecutor’s Office, the engineers Roberto Lucani and Fabrizio D’Errico, during the investigations identified (and through a moral suasion solicited solutions) all the causes for which every now and then a train was transformed into a “ghost”, that is, it was lost by the central system, triggering the safety brakes. In 2019, the “events” were about 300, although most of them did not cause falls or injuries. In M1 the trains communicate with the ground systems every 600 meters: that is, they exchange information about their position with the “buoys”. If everything is OK, the central brain “authorizes” the train to continue its journey. Hundreds of times, in that 2019, however, a train happened to read a mark out of position he should have been in, or read a buoy twice, or lost contact when restarted.
The relocation of Atm trains
All problems that caused the “relocation” of trains, and therefore braking: without ever risking an accident, the experts explain. It has always been just “false positives”. The malfunctions have been resolved by Alstom, but in the meantime, at the end of 2019, the ATM had asked with an emergency procedure to be able to limit the power of the sudden blockade of convoys, using only half of the “skids” (the electromagnetic bars that drop onto the tracks for an immediate stop). The solution made it possible to avoid disastrous falls even in the event of sudden braking, maintaining the same level of safety in circulation. And so, in parallel with a campaign dedicated to passengers to hold on to the supports of the wagons, it eliminated the consequences of the braking, waiting for the suppliers to resolve the causes. The same that Atm had already done previously, independently, dismantling the doors on the docks at «Sesto», which caused constant interference.
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October 26, 2021 | 07:48
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