The project included the excavation of a 13km tunnel, parallel to the existing cross-border tunnel to convert the single tube shield Fréjus tunnel into twin tubes designed for unidirectional traffic. The excavation of the safety gallery, shelters and associated structures were done while keeping the tunnel open to road traffic with a careful monitoring of vibrations on tunnel structure.
The first 650m of the gallery on the French side were excavated using the NATM method, a hard rock TBM with shield was then used to bore the tunnel southwards with a maximum overburden of 2,000m. On the Italian side, the construction of new multifunctional buildings adapted to the needs of the rescue, management and maintenance services.