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Thursday 25 July 2013

Spanish Rail Crash – What We Know

[Update at end of post]

The Speculatron of partially informed punditry has fired into action overnight after a passenger train derailed on the approach to Santiago de Compostella in the Galicia region of north western Spain. At the time of posting, it appears that 78 of those aboard lost their lives, and many more are injured, some seriously. The circumstances appear straightforward; the questions arising less so.
The derailed train was similar to the 130 series - at right

The train that derailed was a Talgo/Bombardier 730 series, consisting of two power heads (one at each end of the train), two diesel generator coaches (one behind each power head), and nine trailer coaches, with a mixture of Preferente (First Class) and Turista (Standard Class) seating. The trains have been rebuilt from straight electric 130 series trains, to enable them to operate beyond the limits of electrification.

The derailment occurred at the end of a newly inaugurated high speed section of track, where the speed limit changes from 200km/h (124mph) to 80km/h (50mph). For some reason, the train does not appear to have slowed significantly, and the resulting overspeed has resulted in its derailment. The coaches do not appear to have stood up to the impact at all well.
As the diagram above shows, the line approaching the point of derailment uses the European Train Control System (ETCS) to regulate trains and their speed. But, and this is the crucial but, ETCS hands over at this point to the older Spanish ASFA system, which also uses conventional lineside signalling. The line is also on a gradually falling gradient.

From this, the question has to be asked: what provision was there in the ETCS installation to slow trains down as they approached the curve on which the train derailed? Was there any provision under ASFA, or would that have been ineffective, given the proximity to the curve? In the UK, there would have been at least a warning, and with many lines nowadays, an overspeed provision.

This last comes via Train Protection and Warning System (TPWS), which has in recent years significantly reduced signal overruns and overspeed incidents. Had there been no similar provision on that part of the Spanish network, it would only need driver error or distraction – or leaving the braking late and encountering slippery rail conditions, perhaps – for disaster to follow.

Following the question of how the train was allowed to do that speed at that point is the apparently poor crash resistance of the coaches. Around a third of those on board died – an utterly horrendous proportion. Talgo trains, in their many incarnations, are part of the railway fabric of Spain, and to see this one apparently fold up so badly is worrying. That, too, is for the crash investigators to pursue.

The best thing that can come out of this is measures to prevent a recurrence.

[UPDATE 1805 hours: I've been pointed at an item in the Público (in Portuguese) which shows the approach from the new line to Santiago de Compostela station.
As can be seen, the new line, which approaches more or less straight for many kilometres, is effectively then tacked on to the existing network to avoid the need to cut a swathe through the city's built up area. This is not necessarily A Bad Thing, providing the approach speed prior to the curve where the derailment occurred is properly controlled.

And here we come back to the two safety systems: whereas ETCS is set up to continuously monitor speed and slow the train if overspeed is detected, ASFA has an inbuilt lag in response. Moreover, the handover point was so close to the curve that ASFA could not have slowed the train in time, given the extent of the overspeed.

The probable solution is to reconfigure the ETCS installation to slow trains before handing over to ASFA control: ideally, the speed at which handover takes place should be synchronised. The presence of a concrete retaining wall will not have helped the survival chances of those aboard, and that is yet another reason to ensure trains are slowed before they leave the new line]


Unknown said...

I'm looking at the dynamics of the accident and wondering if there wasn't a special unlucky circumstance here. From the video (and damage from photographs) the derailment appears to start behind the leading power head, with the first major damage on the rear right of the third trailer. As this is the last car before the bridge, I suspect the fourth trailer was pulled right and smacked the end of the retaining wall or possibly a structure we now can't see before the fourth trailer broke away and headed up the slope to the right. That car must have stopped from 100mph+ in somewhat under 100m, therefore, which possibly explains what appears to be a lot of serious/fatal casualties in that relatively undamaged coach.

Once the rear half had been violently decelerated from the fifth trailer onwards, of course, the momentum from the rear power cars would have jackknifed the lighter trailers, resulting in the pile up before the bridge where presumably most of the casualties were - the brakes would be going on but with the train well off the rails there's no braking effect at all.

Finally the rear powerhead has overridden the presumably fairly flimsy diesel car, crushing it against the start of the retaining wall to such an extent that the engine is resting on the wall and the powerhead itself is cracked from top to bottom. Spilt fuel ignites under the remains, leading to the fire visible in the early pictures.

All in all, too fast and very unlucky with the location - a conventional cutting or somewhere without the hard-ended retaining wall would have probably guided the derailed train to a slower deceleration with more of the cars inline/upright/intact.

So the next question is 'what risk assessment was done before opening a 200kph+ high speed line ending in a hard-edged 80kph bend with no overspeed protection?

Nelson said...

Thales are saying they worked to the tender and installed ERTMS 80km out from Ourense leaving the existing ASFA in place for the remaining 4.3km into Santiago station. ASFA would only trigger the brakes on a red light while ERTMS would do it ahead of the fatal curve.

Tim Fenton said...

Nelson, am I reading the El Pais article correctly - does it say that ETCS is not actually used on the new line between Ourense and Santiago de Compostela?

SteveB said...

I think Tim has put his finger on the more important question, never mind why it happened, why the poor survival rate?

The Virgin Pendolino that derailed at Grayrig in 2007 was travelling at nearly the same speed, it didn't hit a wall but it did fly through the air over a drop and come down hard some distance below. One person died.

In the video the lead loco takes out most of the electrification steelwork (yet the driver survived)and whilst the concrete wall wouldn't do the bodywork any good, it was smooth and shouldn't have had much effect inside the coaches.

One of the survivors mentioned being covered in seats and luggage. There's an alarm bell. Did the seats part from their mountings in the way that airline and British train designs aren't allowed to? Any flying luggage within a coach is often more dangerous than what's happening outside. Which is why British train luggage racks are designed to make it impossible to stow large heavy pieces overhead.

My biggest question is about the trackside camera that captured the crash. Why was it there? Is the Spanish rail network covered in hundreds of cameras like Londons roads? Or was this point being specially monitored for a reason?

Tim Fenton said...

I've wondered for many years about how good Talgo coaches would be in standing up to a serious accident.

The ones used in the 130 and 730 series trains are no doubt an improvement over the original rather flimsy looking Talgo - which in any case had a big heavy diesel loco at the front of it - but don't look to be in the Pendolino and Mark 3 league.