The final project comprises a 57km twin-bore base tunnel between St Jean de Maurienne and Susa with cross-passages positioned at 333m intervals. The cross-border section extends for 18.1km on the Italian side, 12.5km of which will be in the base tunnel. Beyond the Italian portal, there will be a 3km link to the existing line at Bussoleno, including a 2.1km tunnel and a new station at Susa.

The decision to increase the proportion of tunnel reflects concerns over the environmental impact of the project in the Susa area. According to the ministry, the total land area to be occupied by the railway on the Italian side is now less than one hectare.

The approval process in Italy will take several months and will conclude with the final approval of the Interministerial Committee for Economic Planning, which will be followed by the declaration of public utility.

The Italian government has already committed nearly €3bn to construction, of which €840m will be spent during 2013-15 and €150m per year during 2016-2029.