Bouygues Travaux Publics, a member of a consortium with the Soletanche Bachy group and CSM Bessac, is working on the extension of Line 14 of the Paris metro, to the north of the city. Apart from boring a 2.2-kilometre tunnel, the project includes the creation of a new station, Mairie de Saint-Ouen, as well as four ancillary structures, including reinforcing the infrastructures of line C of the RER (Regional Express Network). Forming part of the Grand Paris development project, these works pose considerable technical challenges in a very dense urban environment, particularly taking account of the diversity of soils. This infrastructure project will help to relieve congestion on Line 13, improving travel conditions and access to Paris for people living in the northern suburbs.