Trains may now travel through the Lötschberg base tunnel between cantons Bern and Valais at speeds of up to 250 km/h.
The Federal Transport Office announced its decision on Tuesday after further examinations of security installations inside the 34.6 km tunnel, which was officially opened in December last year.
Since opening, more than 33,000 trains have passed through the tunnel, which was built as part of the New Rail Links through the Alps (NRLA), aimed at shifting North-South transit traffic from road to rail.
The operator of the tunnel, the BLS Lötschberg Railway, has now provided the necessary safety certification papers allowing the higher speed.
In the year since the new tunnel opened, only about 450 trains had to take the mountain route through the old tunnel running from Kandersteg to Goppenstein, because the rolling stock was unsuited to high speeds.
Switzerland is also building the world's largest rail tunnel - 57 km – along the Gotthard route through the Alps as part of the NRLA.