The new tunnel would serve as an alternative route when the main one, a heavily trafficked motorway, closes down to allow for expansion work.
Currently serving as one of the major links through the Alps, the Gotthard tunnel is often clogged with holiday-makers heading south for the summer. The world’s longest rail tunnel will soon run close by, and is scheduled to open to traffic in 2017.
The outcome of the vote was hailed as a victory by the Alpine Initiative and other environmental organisations that aim to reduce road traffic in the mountains.
The groups said in a statement that train shuttles could be considered as an alternative to the second tunnel.