SACEM (railway system)

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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, Matra (now part of Siemens Mobility) and CSEE (now part of Hitachi Rail STS) in the 1980s. It was first deployed on the RER A suburban railway in Paris in 1989.

Afterwards it was installed:

• on the Santiago Metro in Santiago, Chile;
• on some of the MTR lines in Hong Kong (Kwun Tong line, Tsuen Wan line, Island line, Tseung Kwan O line, Airport Express and Tung Chung line), all enhanced with ATO,^[1]
• on Lines A, B and 8 of the Mexico City Metro lines in Mexico City;^[2] and
• on Shanghai Metro Line 3.^[3]

In 2017 the SACEM system in Paris was enhanced with Automatic Train Operation (ATO) and was put in full operation at the end of 2018.^[4]

The SACEM system in Paris is to be enhanced to a fully fledged CBTC system named NExTEO. First to be deployed on the newly-extended line RER E in 2024, it is proposed to replace signalling and control on all RER lines.^[5]