The Grand Paris metro project passed an important milestone. The extension to Mairie de Saint-Ouen of metro line 14, the backbone of the Grand Paris metro project, was inaugurated on Monday 14 December 2020. This extension includes a 5.8 km tunnel and four new stations north of Paris: Pont Cardinet, Porte de Clichy, Saint-Ouen, Mairie de Saint-Ouen. 4 populous municipalities are concerned: Paris (8th, 9th and 17th arrondissements), Clichy-la-Garenne, Saint-Ouen, Saint-Denis, for a total of 96,100 inhabitants and 72,000 jobs served. Grand Paris metro project facts.