Eight years in the construction, the single-track Simplon Tunnel opens in 1906; it is Switzerland's second Alpine rail line after the Gotthard. Almost twenty kilometres in length, it is also the world's longest rail tunnel at the time. Now, western Switzerland is linked to a transit route to the south. Construction is overseen by the private Jura-Simplon-Bahn AG, then the largest rail company in Switzerland. With the nationalisation of the railways, its place is taken by Swiss Federal Railways (SBB). The line is electrified in 1908 and a second single-track bore is completed in 1921.

« The Commission therefore proposes a base tunnel 16,070 m in length in an altitude range from 820 to 830 m. »

Expert report on tunnelling through the Simplon, p. 36, 17.11.1886