It runs under Col du Fréjus in the Cottian Alps between Modane in France and Bardonecchia in Italy.

Temperature sensors were installed at short distances throughout the tunnel, monitored from a central control post.

There are 11 safety points along the tunnel, equipped with telephones and loud speakers connected to the control room, with a separate ventilation duct to supply fresh air.

Despite these measures, on 4 June 2005, a fire caused the death of two Slovak lorry drivers, and the closure of the tunnel to traffic for several weeks.

Work began in 2009, following EU regulations put in place after the Mont Blanc Tunnel fire.

[7] This site houses the Neutrino Ettore Majorana Observatory (NEMO experiment), an international collaboration of scientists searching for neutrinoless double beta decay.

Attempts are underway to build a larger laboratory, either in the same tunnel[8] or in the even deeper Lyon Turin Ferroviaire 15 km to the east.