The mother of all bridges

The world's longest and highest viaduct opens in December. The locals hope it will be their Eiffel tower
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The Independent Online

From a distance, the bridge looks too slender and too graceful to be real, like a row of giant storks standing on abnormally long, fragile legs. Only when you approach the vast, gently dividing pillars do you grasp the scale - but also the elegance and the well-toned, concrete and steel muscle - which will make the Viaduc de Millau one of the engineering wonders of the 21st century.

From a distance, the bridge looks too slender and too graceful to be real, like a row of giant storks standing on abnormally long, fragile legs. Only when you approach the vast, gently dividing pillars do you grasp the scale - but also the elegance and the well-toned, concrete and steel muscle - which will make the Viaduc de Millau one of the engineering wonders of the 21st century.

Forget the Golden Gate, the Sydney Harbour Bridge and le Pont de Normandie. The world has a new candidate for the title of "Mother of all Bridges".

From 17 December - one month early - the tallest viaduct ever constructed will carry traffic across the valley of the river Tarn in south central France, forging an important link in what will (eventually) be a continuous motorway from Paris (and the Channel tunnel) to Languedoc and Barcelona.

The viaduct at Millau, designed by the celebrated British architect Lord Foster of Thames Bank, is, at its highest point, 60ft higher than the Eiffel Tower. It resembles three and a half suspension bridges, chained together on seven immense pillars, striding in a slight curve for one and a half miles between two high plateaux. The tallest pylon over the road-deck reaches 1,125 feet (343 metres) above the valley.

Imagine a bridge joining one range of hills to another. Both the height and the length of the viaduct are records of various kinds but it is the unbearable lightness, even apparent fragility, of the structure that is most startling. The Viaduc de Millau has been designed to use light, strong, avante-garde materials and computerised techniques, to reduce cost and time but, above all, to soften its impact on the rugged landscape of the southern Massif Central.

As it neared completion, Lord Foster said: "Yes, the bridge is extremely delicate, although not in the strength of its construction. We wanted the bridge to look as delicate as possible, unbelievably delicate, in the true sense of the word 'unbelievable', in other words hard for the onlooker to believe. This was a deliberate choice, a response to the fears expressed by many people - quite justifiable fears - that a viaduct would ruin the wonderful landscape of the valley of the Tarn.

"I am delighted that local reaction to the bridge as it has taken shape has been hugely positive. When you think how controversial this project once was, that is extremely gratifying."

Local people and politicians are so smitten by "their" bridge that they hope that it will put Millau (pronounced Mee-oh) on the global map and attract tourists in its own right. "People go to Pisa to see the leaning tower and Paris to see the Eiffel tower. We hope that they will now come to Millau to see the viaduct," said the mayor, Jacques Godfrain. "We hope that Millau will become the theatre from which the spectacle of the viaduct can best be viewed."

Previously, Millau (pop 22,000) was known as the site of the world's most celebrated McDonald's restaurant, destroyed by the French campaigner for small farmers, José Bové, in 1999 as a protest against US trade policy. It was also the location of a huge rally of pro-Bové, anti-globalisation activists the following year.

However, to French holidaymakers, and weary tourists from other nations, Millau has been best known for many years as a crippling bottleneck on a partly completed motorway route through central France to Montpellier, the Languedoc coast and Spain. At this point, the hills of the Massif Central are divided, beautifully but inconveniently, by a broad gorge, up to 1,000ft deep, separating the granite Lévezou plateau from the limestone Larzac plateau, home of the Roquefort sheep's cheese. Between them, the river Tarn has gouged out, over the millennia, France's version of the Grand Canyon.

The A75 Clermont Ferrand-Beziers motorway peters out on the granite cliff-tops to the north and resumes on the 2,500 feet high plateau to the south. The 20 miles of twisting, steep road into and out of the valley can take over three hours to drive, bumper to bumper, in the height of summer. From December, via Lord Foster's Millau viaduct, the journey will take 10 minutes.

Lord Foster, 69, formerly Sir Norman Foster, sometimes called "Storming Norman", is best known for the new Reichstag building in Berlin, the Stirling-prize winning "Gherkin" office building in the City and the Millennium footbridge across the Thames. (The Millennium bridge was utterly different in concept to the immensely larger and more rigid Millau viaduct; both Lord Foster and the Millau engineers say that the "wobbles" which originally afflicted the London bridge, finally traced to the steps up from the river bank, cannot happen here.)

This is the first time that Lord Foster - or any other architect - has been involved in the design of a piece of civil engineering on this scale. So controversial was the plan to bridge the Millau chasm, first mooted in the late 1980s, that the French government stipulated that the project must be shaped by an architect as well as an engineer. Paternity of the bridge is Lord Foster's but he shares overall credit with the man who conceived the idea for a high-level viaduct over the Tarn, the French engineer Michel Virlogeux, head of the French government's bridges and roads department and the designer of the Pont de Normandie across the mouth of the Seine.

The French government's decision, in 1996, to award the Millau bridge design to Lord Foster was also noisily controversial (mostly among French architects). "All the other bidders got hung up with the idea that the bridge had to span the river Tarn," Lord Foster told The Independent. "They all came up with grand structures for crossing the river itself, and gave less thought to what was happening on either side. If you look at the river at that point it is narrow enough to run through my office. From some angles you can't see the Tarn at all."

"I said, when I made my presentation, in public, in Millau, that I was definitely not the person that they should choose if they wanted to build a bridge across the river. I wanted to build a bridge to cross the whole valley, the entire space between the two high plateaux on either side, something that would be elegant and uniform and delicate and take account of the grandeur and sweep of the landscape."

The British architect says that there has been "fantastic co-operation" from the beginning between his team and the French engineers and contractors.

(Whatever other Franco-British quarrels may persist, the official opening of the Millau viaduct on 14 December by President Jacques Chirac will be a fitting way to end the centenary year of the Entente Cordiale.) Engineering and aesthetic, or archi- tectural, choices have intertwined from the beginning, he said. The seven pillars which support the viaduct look tubular and monolithic from a distance but are in fact split into curving, sculpted, gently separating columns, which resemble the fibia and tibula in a forearm. Lord Foster said that the design was partly driven by aesthetics but took account from the beginning of what was possible, and even desirable, from an engineering point of view.

The viaduct, costing €400m (£278m), has been built in record time (just over three years) for a project of this size. The French construction company, Eiffage, the direct descendant of the company started by Gustav Eiffel, the builder of the celebrated tower beside the Seine, has raised the money entirely from private financing. In return, the company has been given a 75 -year concession to run the viaduct as a toll-bridge (likely to charge around €5 per car, €6.60 in the peak summer months).

The deck of the bridge - on which the four-lane road rests - has been constructed from special steel, not from concrete. This is one of the choices which has made the bridge relatively light-weight and so seemingly delicate to the eye.

Eiffage devised a method for preconstructing the 32-metre wide road-deck in 2,000 pieces at its factory in Alsace. They were welded together on the hills on either side of the valley and then shoved out over the abyss 60 centimetres at a time. Roughly one mile of decking was pushed out from one side; half a mile from the other.

Satellite positioning technology ensured that the two ends connected correctly (at the end of May). While this was going on, enormous, temporary trestles were built from the valley bottom to prop up the roadway.

Once the "deck" was completed, A-shaped steel pylons or masts were constructed up to another 90 metres above the road level to hold the cables which support the bridge. As the cables have been attached in recent weeks, the temporary trestles have been taken away, leaving the roadway suspended spectacularly for 350 metres between each pair of pillars. Millau is the highest viaduct in the world. It is also the highest bridge in the world if you measure the distance from the valley bottom to the peak of the pylon above the highest pillar (343 metres or 1,125 feet).

Counter-claims can - and no doubt will - be made. The road level of the Millau viaduct is 270 metres above the Tarn at its highest point. At "only" 885 feet this is somewhat lower than the road which crosses "the world's highest suspension bridge", the Royal Gorge Bridge in Colorado. The American bridge has a roadway 1,053 feet above the river but it is much shorter and narrower than Millau and not so tall to the top of the highest suspension pylon.

Lord Foster says that his design for Millau plays with the "tension" between the "delicate, thin band" of the road deck and the "extraordinary height of the pillars". (Number P2, rising from close to the Tarn itself is, at 245 metres, the tallest bridge pillar ever constructed). Lord Foster also said that he intended the viaduct to "exploit the contrast" between the "disorderly, savage, natural landscape on either side and the uncluttered, simple, obviously human-inspired lines of the bridge."

"I had many awkward choices. There was the question of what colour we should use on the suspension cables. Should they be dark brown, so that they blended in, and disappeared, when seen against the hills, making the bridge look as if was standing up as if under a spell?''

"Or should they be light-coloured so that they would virtually disappear from a distance - not look too clunky - against the sky?" Lord Foster chose the light colour.

"The first time that I went to see the bridge when it began to take its final shape, I was very nervous. Had we made the right choice? You can never be quite sure how things are going to look. When I saw it, I had a fantastic sense of relief. Yes, that was what we wanted."

Lord Foster hopes that the Millau bridge will go down as an important advance in the engineering of bridges but also in the aesthetics of bridges - a practical argument for his belief that architects, not just engineers, should be involved in civil engineering projects. "I've been saying for a long time that our lives are largely shaped by our infrastructure and we should therefore take care of what our infrastructure looks like. That is the subject of a talk that I am giving shortly in Madrid."

Lord Foster is also anxious that "his bridge" should retain its grandiose, natural setting. He fears that the popularity of the viaduct - and the determination of local politicians to attract tourists - may result in a kind of strip-mall in the valley beneath the bridge.

"I am not at all opposed to there being a visitor centre and that the temporary roads built to help construct the bridge should be retained if they are really needed. What I would not like to see beneath the bridge - and I have been quite firm about this - is the kind of sprawl that you see on the edge of so many French towns." A public inquiry has been ordered to consider this question and will report in December, at about the time the bridge opens.

What will not be ready for the opening date - and will not even be ready for the first big tourist rush over the viaduct next summer - is the rest of the A75 autoroute to the south coast. As a result of planning delays, the road onward from the bridge - performing a series of spectacular bends from the high plateau down to the coastal plain - is far behind schedule.

The last sections, linking the A75 to the A9 south coast motorway, at Montpellier and Beziers, have not even been started yet. In other words, the perennial traffic jams around Millau are likely, for several years, to be transferred 60 miles to the south.

None of that is Lord Foster's pr oblem. Will he be in Millau on 17 December for the opening of his bridge? "Nothing would keep me away."