Why not use the existing access roads to the Train Maintenance Workshop (Fontenay tunnel) to carry out the extension?

In addition to the tracks used daily by the trains transporting passengers, the Paris metro has a set of technical tracks that are used to store trains, maintain them or access maintenance centres. These tracks, which are essential for the proper functioning of the metro, cannot be used and have not been designed for passenger transport. The M1 has technical tracks to the west, at Porte Maillot, and to the east, after Château de Vincennes, with a rear station for parking trains when they are not in use and access roads to the Fontenay train maintenance workshop.

These existing tracks, which are 3 in number at the back of the station and then reduced to 2 and then to 1 track, are technical tracks: they serve as access to the Train Maintenance Workshop (AMT of Fontenay). This workshop provides preventive maintenance for all the rubber-tyred metros on the Ile-de-France network (M1, M4, M6, M11, M14 to date), as well as at the garage of some of the Line 1 trains during off-peak hours, in the evening and at night on Line 1.

The expansion of this tunnel with one or two additional tracks would significantly degrade the operation of several metro lines, or even lead to their complete stoppage. It would lead to:

- the closure of access to the Train Maintenance Workshop during the works, making it impossible to maintain all the tyred trains maintained in this workshop, with unacceptable impacts for users on the operation and quality of service of the 6 metro lines concerned. This maintenance interruption with a regional impact cannot be envisaged.
- the construction of an open-air connection structure for the extension to Les Rigollots (the access roads to the AMT being at a shallow depth) in an urban fabric already constituted on the border of Vincennes/Fontenay with a land impact and a significant additional cost. This would not be accepted by the cities of Vincennes and Fontenay sous Bois.
- the removal of existing storage spaces for the M1 trains, which would have to be recreated elsewhere by extending the rear station, with other urban impacts and a significant additional cost for the project which would call into question the very principle of its realization.