Very Cool

Much has been written about the recently opened Millau Viaduct in the south of France, both here and elsewhere. It takes the form of statistics: 245m from the foot of the valley to the deck, 343m from the foot of the valley to the top of the towers, 2.5km long in total. A cost of €394m to build.

Going out of my way to see the great bridges of the world is something that I do, and after reading all this I was struck by a strong urge to go and see the bridge for myself. So, I flew to Toulouse this last weekend. I rented a car, and headed for Millau. I was in no hurry. I stopped for a pleasant lunch in Albi, and rather than going up the main road, I then wound along the litte roads following the Tarn valley. One thing became obvious quickly. The Tarn valley is a huge gash through the south of France, going for hundreds of kilometres. There was clearly no easy way to build a motorway across it, anywhere. The immensity of the new viaduct was clearly out of necessity.

I had some thoughts of following the Tarn river valley all the way from Albi to Millau, with the idea that I would appreciate the scale of the valley, finally glimpse the viaduct in the distance when I was a few kilometres from it, (or maybe tens of kilometres, depending on the geography), and then approach it and eventually drive under it.

As it happened though, this was not quite what happened. The drive up the valley was spectacular, but it was a difficult drive, due to a narrow road (with some very lengthy narrow tunnels from an earlier era of engineering), and some awkward driving conditions. (It was very cold. Much of the river valley and even some of the road was covered in snow). And I kept stopping due to the fact that the scenery was beautiful and at times remarkable. (The small village of Ambialet, built in a truly extraordinary curve in the river, kept me for some time, as did a few other places).

This part of France had an odd feeling of abandonment about it though. There are a lot of small villages along the river, containing beautiful old stone buildings, but these contained very few people and. I get the impression that the valley was a (fairly marginal) agricultural location a generation or two back (potatoes I would guess) but that is now gone. There are a few shops in the villages but these were mostly closed. The permanent population of these places appears to be small, and demographically not especially young. The buildings are generally in good repair, however. I get the impression that this place is highly seasonal. Tourists and owners of holiday homes probably come in summer in huge numbers for canoeing, kayaking, hiking, hang-gliding and various other activities, but not in the winter. Which is a shame, because in winter under the snow the valley was beautiful. But to attract people in winter you need to offer skiing, and this is not skiing country.

But on to the bridge. After several hours of driving slowly and stopping regularly, I realised I was a bit fatigued and it was getting late, so I ended up diverting to the B999, the main road to Millau, which detoured over a couple of ridges rather than winding up the valley.

And oddly, this turned out if anything to be better than the original choice. For as it approaches Millau the B999 swerves back into the Tarn Valley and goes under the viaduct into Millau. But it doesn’t do so at the foot of the valley but along one of the sides of the valley, probably about halfway up in altitude.

As it happened, I didn’t see the viaduct until I was quite close to it when I came around a curve in the valley. I could only initially see a small portion of it, but it was a long way above me. I drove closer, and more of the viaduct became visual. Directly under it was a visitors centre, so I parked the car and looked around me. I looked down at the river, and one of the supports of the viaduct receded a huge distance downwards. I looked to one side of the valley. The viaduct receded into the distance.

I looked the other way. The viaduct receded a long way into the distance that way, too.

The legs of the viaduct are thick and emormous, but the deck looks somehow very slight, still somehow being held in the air when it probably shouldn’t. The materials from which this bridge has been built are vastly stronger than anything that existed even 20 years ago. I have said this before, but this is in my mind the defining characteristic of modern post materials revolution structural engineering. Structures are then, flimsy. They almost look like spider webs. The defining characteristic of industrial age engineering was bulk. But now we are in this virtuous circle of stronger and lighter materials allowing a much thinner deck, allowing the other parts of the bridge to be lighter and less substantial too, allowing still more economies elsewhere, and a rapidly dropping cost of projects like this.

And this is why this viaduct has been built. One upon a time there was only one way for a road to cross such a valley, which was to have a road going down a steep winding pass into the valley, crossing the river, and then coming up another steep winding pass on the other side. And this isn’t compatible with a motorway.

To build a straight motorway across such a valley there are two options: you dig tunnels through the cliffs on either side of the river to bring the road down to something close to river level and have a low level bridge, or you build an immense high bridge. Until recently, the cost of both options was prohibitive. Building tunnels probably still is. But due to the materials revolution the cost of a high bridge has been plummeting.

And here is the deal. Given the immensity and magnificence of the structure, the €394m that the viaduct cost to build actually wasn’t very much. Given that this is the main road from Paris to the south-west of France and to Spain, one feels that toll collection will pay off the construction cost fairly easily, even if the toll (€6.50 in summer, and €4.90 at other times of year) seems cheap.

In any event, I drove into Millau, stopping at a vantage point for another view.

But to really get an impression of the size of this thing, it’s worth standing at the very bottom, as I did the next morning. This is high. (It’s unfortunately very difficult to take a photograph that captures both the length and the height of the bridge. It tends to be one or the other.

It’s easy to make smaller structures look like this with a camera and the right lens, but I am not doing this. If anything, these photographs understate the scale of the bridge. I actually took these photographs from the bottom of the bridge at around 10am on Sunday morning. As I was standing below the bridge, it appeared to start raining. This was odd, as the sky was completely clear. It took me some time to figure out that the “rain” was in fact overnight frost that was melting on the bridge way way above me and that was falling onto the floor of the valley.

But of course a bridge needs to be crossed. I like to walk across bridges, but it is not really possible with this one. It is long, and the starting and finishing points are too inaccessible. So I paid the toll, and drove over it. No doubt I broke several French laws by taking photographs while I was driving, but I did.

The towers and cable stays are surprisingly small given the size of the bridge. Also, on most cable stayed bridges the stays connect the towers to both edges of the bridge. Here, there are a single set of stays connecting to towers to the median strip between the two traffic ways. The deck is clearly stronger and more rigid than decks were even five or ten years ago.



And to make sure people are not spooked by the height that they are travelling above the valley (and presumably to also stop people from jumping) the barriers at the edge of the bridge are pretty substantial.



Impressive, yes, but get used to this kind of thing. Of the various computer driven technological revolutions that have been occuring in recent years, the revolution in materials is one of the most important and yet this one has received less publicity than most. Which is a shame, as this is the one that is about our control of the physical world. Architecture has become more playful in recent years, very much because engineers are suddenly less constrained by the tolerances of materials than they were. Structures of unprecedented size and length are becoming possible, at dramatically reduced costs. Some of the structures we will see in the next twenty or thirty years will boggle the mind. It’s a very exciting time to be alive.