Système d'aide à la conduite, à l'exploitation et à la maintenance

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SACEM cab signalling (far left) on the MI 09, showing a speed limit of 100 km/h (62 mph)
Lineside signal on RER A taken over by SACEM, as indicated by a St. Andrew's Cross (⨯)

The Système d'aide à la conduite, à l'exploitation et à la maintenance (SACEM) is an embedded, automatic speed train protection system for rapid transit railways. The name means "Driver Assistance, Operation, and Maintenance System".

It was developed in France by GEC-Alsthom and Siemens in the 1980s. It was first deployed on the RER A suburban railway in Paris in 1989.

Afterwards it was installed:

In 2017 the SACEM system in Paris was enhanced with Automatic Train Operation (ATO) and will be put in full operation until end of 2018.[3]

The SACEM system in Paris is to be enhanced to a fully fledged CBTC system named NExTEO. First to be deployed on the new prolongated line RER E in 2024, it is proposed to replace signalling and control on all RER lines.[4]


SACEM cab signalling on the MI 2N Altéo in "Jog Mode", showing a speed limit of 30 km/h (19 mph)

The SACEM system enable a train to receive signals from devices under the tracks.[5] A receiver in the train cabin interprets the signal, and sends data to the console so the driver can see it. A light on the console indicates the speed control setting: an orange light means "Jog Mode", or 30 km/h (19 mph); a red light means full stop. If the driver alters the speed, a warning buzzer may sound. If the system determines that the speed might be unsafe, and the driver does not change it within a few seconds, SACEM engages the emergency brake. SACEM also allows for a reduction in potential train bunching and easier recovery from delays, therefore safely increasing operating frequencies as much as possible especially during rush hour.


  1. ^ Wong, Marcus (2011-04-12). "Railway signalling on the MTR underground". Checkerboard Hill, Private blog. Retrieved 2017-12-23.
  2. ^ "Mexico City (Mexico) Lines A, B and 8 - SACEM high performance Automatic Train Control for driver-based operation" (PDF; 600 kB). Siemens SAS; Infrastructure & Cities Sector; Mobility and Logistics Division. 2015-03-05. Retrieved 2017-12-23.
  3. ^ "Alstom-developed Automatic Train Operation system successfully enters service on the RER A". ALSTOM Holdings. 2017-10-05. Retrieved 2017-12-23.
  4. ^ "RER E – soon one train ahead thanks to NExTEO …". SNCF Réseau. 2017-07-20. Retrieved 2017-12-23.
  5. ^ "Système d'Aide à la Conduite, à l'Exploitation et à la Maintenance". Institution of Railway Signal Engineers. 2003. Retrieved 2017-12-23.

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