Friday, July 26, 2013

Design and death

In Spain’s worst rail disaster in almost 70 years, 78 people are dead and 32 are in serious condition.

The high-speed ALVIA service uses a preexisting tight curve at that location, three km south of Santiago de Compostella on the Madrid-El Ferrol line. Straightening the route would have been costly, so train drivers are required to slow sharply from 200km/h to 80.

Train drivers, like car drivers, often do not do as they should. On Spain’s dedicated high-speed lines, as in many other parts of Europe, a system named ERTMS would then apply the train’s brakes. But there was no ERTMS on this section of the route, nor any alternative automatic breaking system triggered by excessive speed, such as that used extensively in the U.K. (following a spate of horrific accidents there). Instead, Spain’s old ASFA signaling system was used, which merely informs the driver that he should slow down. But the driver hadn’t been paying adequate attention.

So the driver’s failure to slow down in time on a tight curve such as this automatically and ineluctably led to an accident. It was then up to the design of the rolling stock to minimize the harm from the result.

There is a best-practices design that has successfully done this for 32 years, with only two fatalities on a single train. It is Alstom’s TGV, used in several countries including, ironically, Spain’s own first high-speed line between Madrid and Seville, where they still run. Adjacent carriages are joined by rigid membranes and ride common bogies (trucks). The entire weight of the train acts to keep every part of it upright. It also prevents the carriages from jackknifing (folding on each other), as happened both in Spain and in the similar accident in Germany in 1998. The carriages’ departure from the track at high speed into a concrete wall, their falling down on their sides, and their jackknifing were major contributors to the carnage.

The Bombardier-Talgo S730 trainset that crashed in Spain represents a nod to some of those principles but not enough of them to prevent a bloodbath. It does have a low centre of gravity. It is not made of aluminium extrusions; those tend to tear along the windows like stamps along perforations, and apparently contributed substantially to the toll in the German ICE accident. However, it is made of light aluminum that shattered on impact, the car ends were torn from their tilting suspensions, and the aft gas turbine generator engine was thrown from its dedicated carriage, landing in its entirety on the embankment above. It does use joint bogies, but these do not by themselves guarantee stability or integrity in the absence of perhaps the most important safety factor: rigid membranes between carriages. On the S730, the latter are fully articulated as on a conventional train. They are free to fall on their sides, fly into walls, collide with each other and fold like harmonicas.

This was not, as many terrible accidents are, the result of an unlikely combination of factors. Rather, this was a blatantly design-caused, foreseeable disaster. It would be unfair to say that nobody cared. However, by default we all labour under an overwhelming weight of lack of awareness of the meaning of our choices. Here, people from four companies — the train operator RENFE, track owner ADIF, Bombardier and Talgo — allowed a design to be developed and placed into service that relied entirely on the driver’s slowing down when entering that curve. If he did not pay full and timely attention — as they themselves had failed to do — or the train’s braking system failed, there would be no automation to stop him and nothing to prevent a terrible outcome.

No comments:

Post a Comment