Experts from the canton of Uri, at the head of the valley leading to the St Gotthard tunnel, said it would take days to assess whether the explosion would eliminate the danger of severe rockfalls that last month closed the A2 motorway.

The closure of the four lane route, and of the parallel, older road over the pass, has led to traffic chaos. Heavy goods vehicles that ply the Gotthard, one of the most convenient routes between northern and southern Europe, have had to seek alternatives, leading to massive congestion.

The cause of the diversion happened on May 31, when giant boulders crashed down onto the A2 at Gurtnellen, just north of the 16km-long Gotthard tunnel. Two Germans died when boulders hit their Volkswagen Beetle convertible.

Swiss engineers now hope that the motorway and pass road will reopen in time for the July 1 weekend rush, when thousands of northern Europeans head south for their holidays. But none were willing to make a firm prediction on Friday.

As with the closure of the Mont Blanc tunnel between France and Italy after a fire in 1999, the blockage has spotlighted the fragility of Europe?s transalpine routes - and the crucial logistical role they play in a now virtually single market. In the EU's integrated economy, vast quantities of goods travel between member states - the overwhelming majority by road in 40-tonne trucks.

"The Gotthard has been a crossing point for centuries, whether by donkey, coach, train or, nowadays, motor vehicle," says Markus Z?ead of construction for Uri and the man leading the repairs. The narrow crossing accounts for about 1m of the 1.3m heavy trucks that pass through Switzerland every year. In neighbouring Austria, the Brenner pass between south-eastern Germany and northern Italy is even more vital, carrying 4.5m trucks last year.

"The number of heavy trucks was 5 per cent up on 2004. That's a huge burden for us," says Marc Zimmermann of Asfinag, Austria's highways operator.

At peak periods, about 3,500 juggernauts a day rumble up the narrow Reuss valley towards the Gotthard tunnel. After a fire in 2001 that claimed 11 lives, numbers have been regulated, with trucks being detained in up to five holding areas along the route to prevent the bunching deemed to be a safety hazard inside the world's longest road tunnel.

With the Gotthard shut, it is Switzerland's other alpine crossings that are bearing the burden. Most affected has been the San Bernardino, the closest alternative.

Steeper, bendier and narrower than the Gotthard, the route has been seen massive congestion as the number of heavy trucks has quadrupled from the average 500-600 a day. Shorter jams have also occurred along the Simplon pass, where the number of trucks has risen fivefold to about 750 a day, and the Grand St Bernard pass and tunnel, Switzerland?s two other main transalpine arteries. Even heavy goods traffic using the Mont Blanc tunnel has increased by 12-15 per cent. None of the alternatives is adequate. The Gotthard is the easiest and most convenient crossing?, admits Thomas Rohrbach of the Federal Roads Agency in Bern.

But even when the Gotthard reopens, the chances of a significant improvement in cross-border road links will remain slim because of the acute environmental and financial sensitivity of traffic in the Alps.

?We have to transfer more goods to rail in the long term?, says Isidor Baumann, head of the economics administration for Uri.

Ideas for new rail links abound. But few of the mooted projects seem likely to become reality. Plans for a long rail tunnel between Lyon in France and Turin in Italy are advancing. But Austria?s hopes for a rail link beneath the Brenner are no closer to realisation than ever.

The Swiss, ever sensitive to accusations of benefiting from their proximity to the EU without contributing adequately in return, argue they are about the only ones taking action.

Massive tunnel boring machines are inching their way under the Alps for new crossings in western Switzerland and under the Gotthard. The western link should open in December 2007.

The two schemes will cost almost SFr20bn ($16bn, ?13bn, £9bn) ? with the final bill likely to be higher by the time the 54km Gotthard rail tunnel, the second and more ambitious scheme, opens in 2017. Whether more goods will forsake the roads in favour of rail by then is another matter.