Why not extend line 9 instead?

Additional elements of analysis were provided by Île-de-France Mobilité on this alternative during workshop No. 1 on 12 October 2026 on socio-economic issues and alternatives to the project:

• The extension of line 9 included in the regional planning documents and currently under study is aimed at Montreuil Hôpital, to serve other districts of Haut-Montreuil and to seek a connection with line 11. This route would not serve Grands Pêchers, Les Rigollots or Val de Fontenay.
• An extension of metro line 9 to Val de Fontenay should take into account its current rear station, facing northeast, the radii of curvature of the tunnel boring machine and the passage under the future metro line 15.
• With an extension of metro line 9 to Val de Fontenay via the Grands Pêchers station planned for line 1, the route would reach 5.8 km compared to 5.1 km for line 1, for an equivalent or higher cost; a more direct route (4.8 km) would require a perpendicular Grands Pêchers station, with more land impacts.
• In both cases, line 9 would not serve Les Rigollots, i.e. about a third of the area that would be served by the line 1 extension project. The journey to Paris would be longer: for a comparable cost, the time savings would be less and the socio-economic balance would deteriorate. There would also be land impacts at the level of the Montreuil City Hall, to be compared with the impacts of line 1 in the Bois de Vincennes.

These elements are specified in the presentation material projected during workshop 1, available online on the project website.