Line 2 of Nice’s tramway, with its 3.2 km long tunnel, is characterized by sections of low visibility. For operational safety, these zones are to be protected from inadvertent crossing of restrictive signals (running red lights). In this context, CLEARSY has developed a new version of KFS, its automatic train stop system. This version contains an innovative braking system aimed at significantly limiting the number of emergencies stops when these are not essential to passengers' safety. This system became operational early last summer at 2 out of the 5 stations to be equipped. Eight protection zones are now covered by this system; in the end CLEARSY will equip around 20 protection zones.
"Emergency braking is obviously brutal since it occurs over a very short timescale", explains Florent Patin, project manager. The braking, which would normally be triggered by the driver, is now automatically applied by KFS and occurs within a few seconds of the train passing restrictive signals such as red lights or temporary restrictions. "A KFS system includes three parts, says Patin: a beacon implanted on the track connected to a signal; an on-board sensor fixed to the chassis which captures the information issued by the beacon; and an on-board calculator which sends orders to the train, including the emergency braking". Usually when this type of system is not able to ensure its protective function (when it is in a faulty state) the emergency braking is the default condition. This is extremely uncomfortable for passengers.
"We wanted to have two possible responses to a system failure, to allow the possibility of gentle braking", continues Florent Patin. To make this happen, a failure diagnostic function had to be implemented and the system architecture modified by addition of a 'service braking' output from the on-board software block intended for the vehicle. The Nice solution reserves the emergency braking for situations with immediate risk to passengers. For example, a failure that would not hide the fact that a restrictive signal has been passed would be treated by service braking without risking passenger safety. The final proof is that the system has obtained SIL 2 certification.
In the course of this project, Mobility Crossway (VINCI Energies), a specialist in safety systems for transport infrastructure, developed the signalling system for the line and ordered the automatic train stop system from CLEARSY.