The northern extension of line 14 is mainly aimed at alleviating the passenger saturation of line 13. Four new stations have been built: Pont Cardinet, Porte de Clichy, Saint- Ouen, Mairie de Saint-Ouen, connected by 5.8 km of tunnel tracks. It serves some 96,000 additional inhabitants in the districts of Clichy-Batignolles and the inner suburban towns of Clichy and Saint-Ouen-sur-Seine. The Porte de Clichy station, emblematic of the extension, is located at the base of the new Paris judicial tribunals and serves as the connecting point with metro line 13 and the suburban line of the RER C.
The project developed in the midst of urban density. The presence of other ongoing projects, on the edges and above, required co-conception and joint activity with these construction projects. The great depth needed for the platforms required they be very thickly moulded (1.5 m) over more than 30 m in height. Supplying the materials to this low depth was difficult, in particular with regard to the escalators. The installation of certain elements, such as laying the tile on the walls, required putting up cathedral-style scaffolding.
The structural principle relies on vertically moulded walls, stabilised by horizontal stays and slabs. The walls were poured first, after which the interior earth was dug out to create a volume 30 meters in height, 130 meters long and 22 meters wide. The great depth, the main constraint the project faced, structured the site with regard to the positioning of the stairwells. Relatively bare, the great main spaces were organised and designed based on rational principles of simplicity and robustness.