By Imogen Foulkes
BBC News, Berne
For centuries, the Alps have served as a natural trade barrier between northern and southern Europe.
The new link will cut Zurich-Milan journey times dramatically
Sending Italian wine to the Netherlands, or German washing machines to Greece, means a long, slow journey along narrow alpine valleys, through tunnels and over passes.
The amount of freight crossing the Alps in heavy goods vehicles has risen sharply over the last two decades. In 1990 an estimated 40m tonnes went by road, in 2001 that had risen to 90m tonnes, with further big increases expected by 2010.
But concerns for the Alpine environment and fears over safety have led to big pressure to move freight off the roads and onto the railways.
Both Switzerland's Gotthard road tunnel and France's Mont Blanc road tunnel have suffered major fires in the last 10 years in which many died.
Faster than flying
As long ago as 1994, the Swiss voted in a nationwide referendum to put all freight crossing their country onto the railways. Naturally, such an ambitious plan was not going to happen overnight, but now the project dubbed the engineering feat of the 21st Century is slowly taking shape.
Deep beneath the Alps, the Swiss are building a high-speed rail link between Zurich and Milan. It will include, at 57 kilometres (35 miles), the world's longest tunnel.
A key feature of the project, which is new to alpine transport, is the fact that the entire railway line will stay at the same altitude of 500 metres (1,650ft) above sea level.
This will allow trains using the line to reach speeds of 240km/h (149mph), reducing the travel time between Zurich and Milan from today's four hours to just two-and-a-half. That would make the journey faster than flying.
To see the work in progress, it is necessary to travel two kilometres underground, to the construction site between the southern Swiss towns of Faido and Biasca.
The scale of the work going on is enormous: 2,000 people are working on the tunnel, 24 hours a day, 365 days a year. Besides the two main railway tubes, the construction workers have to dig access tunnels for people and equipment.
Huge fans ensure a fresh supply of air and cool things down. Yet the temperature is above 30C.
"We've got two-and-a-half kilometres of Alps above us," explains engineer Albert Schmid. "That means millions and millions of cubic metres of earth pressing down on us, that increases the pressure and the temperature."
It also means that every time the workers dig out another few metres of the tunnel, mother nature tries to close it up again. Along the tunnel's length, reinforced steel rings have to be inserted, to prevent it collapsing in on itself.
Building the tunnel requires a variety of techniques. At one section the workers are blasting away the rock, and the air reeks of ammonia from the explosives.
At another section the world's biggest tunnel-boring machine is in operation; it is ten metres in diameter and covered in dozens of rock-cutting blades, which as the machine turns, hack away at the rock face.
"With this machine, in good conditions, we can excavate 40 metres in a day," says Mr Schmid. "That's an absolute record."
But conditions are not always good. The tunnel workers have run into serious geological problems; in some areas the rock is as soft as butter, making digging it out more complicated.
"In poor rock conditions, where the rock is very soft, we can only excavate around half a metre a day," says Mr Schmid. "So in these situations, the work is delayed, and the costs rise."
In fact the price tag for the entire rail link has soared from about $8bn (£4bn) to almost $15bn and final completion is unlikely to be before 2018.
But that has not stopped the alpine communities from supporting the project, and from trying to ensure that the rail link brings some social benefits too.
The tiny village of Sedrun, population 1,500, lies along the tunnel's route, and while residents are pleased to be relieved of the heavy lorries, they are concerned that the tunnel may marginalise their community.
"The thing about this tunnel is that it makes the Alps disappear," explains local architect Arthur Loretz. "At the moment, when you drive from Zurich to Milan, you get a beautiful panoramic view. But this tunnel turns the Alps into a big black hole."
The original plans for the tunnel involved trains rushing beneath the Alps without stopping. But in Sedrun a 1,000-metre elevator and underground railway station have been built just to get the workers to the construction site.
"All the infrastructure is already there," points out Arthur Loretz. "What we want to do is use it in the future." The plan is to create a station, deep in the mountains, known as "Porta Alpina" (Gateway to the Alps).
Tourists will be able to arrive by train in the Alps in record time, and then be whisked up to fresh mountain air by way of the world's longest elevator.
"I think it will have great benefits," says Mr Loretz. "Not just for tourists, but for us. Look, over that mountain people speak Italian, and over that one there they speak German."
"And here we speak Reto Romansch - a language only spoken by around 50,000 people. Traditionally the mountains have divided us, but with this rail link, and with Porta Alpina, we can bring people together."