Marseille Subway – CLEARSY delivers an innovative system to secure the terminus of line 2

22 July 2020

Marseille Subway: CLEARSY delivers an innovative system to secure the terminus of line 2.

The dimensions of the tunnel at the new Capitaine Gèze station in Marseilles, the terminus of line 2, prohibit conventional speed and zone control systems by track circuit. This is why CLEARSY has developed and installed a system adapted to the particular configuration of the future terminus of line 2 of the Marseille metro. Objectives: to prevent the risk of overspeed and the risk of derailment when passing a switch.

A two-track derailment is the derailment of a train with cars travelling on different tracks when a switch point is passed. The “track circuit” detection system eliminates this risk by preventing the switch points from moving as long as a train is detected in the area in question. In France in particular, it is the basis for all metro, train and tramway signalling. But it is another device, developed and installed by CLEARSY, which guarantees the safe detection (SIL4) of trains in the area managed by the track circuit at the Capitaine Gèze station in Marseille. The explanations of Patrick Sauvage, director of activities at CLEARSY.

The principle of a “track circuit” type detection system is as follows: When a train enters the portion of track managed by a track circuit, the contact of the rail wheels with the rails triggers a short circuit which causes a normally closed relay contact: this is the information of the presence of a train. In Marseilles, a metro on wheel tyres, it is the wipers placed on the axles that ensure contact with the rail. In these configurations, a signalling rule imposes a minimum distance between the limit of the track circuit and the tip of its switch point. In order to apply this rule, which guarantees the detection of the train in the event of the loss of the first wiper, it would have been necessary to extend the tunnel by 15 metres. Unthinkable. This is why we have installed a device (axle counter) which counts the wheels entering and counts the wheels leaving the area under consideration. The alternative is the same safety level as the track circuit solution. Specially developed for Marseille by CLEARSY, the system is adapted to the 7 cm flange guide specific to wheeled trains.

Indeed, in Marseille, as in Paris, the trains run on wheels equipped with pneumatic tyres, lined with wheels of a slightly smaller diameter, made of steel. These do not, in principle, touch the rails. Safety wheels are also used to guide the train through the points. It is these wheels that are detected by the CLEARSY axle counter.

The second function performed by the CLEARSY system is the detection of overspeeds. The system: an electronic board connected to the wheel sensors which measures the speed of the train. Two measuring zones. If the recorded speed exceeds 16.7 km/h – speed defined by the calculation of the stopping distance – the train is stopped. Otherwise, it would collide with the collider at the bottom of the tunnel.

Certified SIL4 for zone detection, the system successfully went into operation in December 2019. Since the opening of the station, all the system’s sensors have counted more than one million wheels without a fault.