Miriam Behrens of the Pro Natura organisation says a second tube would cause jams to build up elsewhere, and, potentially, add to them.

BBC: St Gotthard tunnel fire

Ms Behrens also says the Avanti proposal would contradict an earlier referendum which made it part of the Swiss constitution to aim to transfer as much freight transport as possible to rail and not to disturb the Alpine landscape for transport.

BBC: St Gotthard tunnel fire