The tunnel should ease the big burden of transalpine traffic

It will cut the journey time between Germany and Italy by at least a third.

It is set to be fully operational in December, and will eventually handle about 42 passenger trains and up to 80 freight trains daily.

The estimated cost of the project is 4.3bn Swiss francs (£1.75bn; $3.5bn). Construction started eight years ago.

Worldwide the Loetschberg is third in length, behind Japan's Seikan tunnel and the Channel tunnel, both of which are underwater. But it is the longest tunnel on land.

Switzerland acts as one of Europe's major junctions for freight and the tunnel is meant to move cargo off the roads and onto rail.

More than 4,000 heavy lorries cross the Swiss Alps by road every day, leading to traffic jams, air pollution and accidents.

The Swiss rail tunnel project - including a second, parallel tunnel, due for completion in 2015 - is one of the biggest engineering projects in the world. Millions of tonnes of rock have to be shifted.

The second rail route, the Gotthard rail tunnel, will measure 60km - making it the longest in the world - and will cut the travel time from Zurich to Milan to only two-and-a-half hours.