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Tilting trains will be tightly circumscribed
This column occasionally writes at length on topics that I am sure readers at the time, think a bit recherché. But trust me, because most times the recherché becomes a matter of commercial or technical life and eath.
Take the March 1999 column and the item about Railtrack's draft Group Standard for high speed operation and tilting trains. There we were thinking of sticking differential speed limit boards at the approach to curves saying ‘Pendolini flat out' when what Railtrack had in mind was quasi ATP with intervention should a driver approach a curve too fast.
Then, in August 1999 this column reported that Railtrack seemed to have suffered a rare outbreak of spontaneous common sense.
It was expected that each curve would be assessed for the risks associated with what are termed ‘Enhanced Permissible Speeds'(EPS) for tilting trains. In most cases, it was thought that lineside differential speed limit boards would be adequate.
Where the speed reduction meant that a missed braking point could make the risk of overturning unacceptable, permanently energised Train Protection & Warning System loops would be fitted. These would trip an overspeeding Pendolino, while a train at line speed would be unaffected.
Hah! Much too easy. What if a driver accelerated after passing the TPWS loop? Why should he do that? Oh it's a safety thing.
Now we have TASS – short for Tilt Authorisation & Speed Supervision. Virgin, and anyone else wanting to run tilting trains on Railtrack, is going to have to fit European Train Control System equipment in the trains and balises on the track – now.
‘A' is for ‘Authorisation'. While Railtrack doesn't know much about its infrastructure is pretty sure that at some places a tilting train could go out of gauge – or whack another train if the tilt failed wrong side.
So the first thing TASS will do is tell a train that it is safe to tilt. If the train passes over a balise and doesn't get this message it will lock itself upright until it hears otherwise. This raises sundry issues to be covered another time – like how do you know that both units of a multiple Super Voyager have got the message?
‘SS' is for ‘Speed Supervision'. The EPS for each curve will be indicated to the driver by lineside speed boards. But since tilting train driver's can't be trusted to comply with speed boards, unlike drivers of boringly ordinary trains, TASS will intervene if the driver fails to slow.
How will this be achieved?. Standard ETCS Eurobalises will be spaced at roughly 5km intervals.
Eurobalises transmit ‘packets' of data – think of them as coded telegrams, and those nice Eurocrat signal engineers have set aside Packet 44 for non European Train Management System functions. Like TASS.
So each TASS balise will transmit two messages in Packet 44. Tilt authorisation and the line speed profile ahead, including any EPS.
On the train, the ETCS equipment will switch on the tilt system if authorised. No, I don't have the detail.
A processor in the on-board kit will take the speed profile, generate a braking curve based on the current speed and if the train doesn't slow as required warn the driver. If that doesn't have the desired effect the brakes are applied.
When the WCML linespeed becomes 125mile/h in 2002, the effect of tilt will be to make many EPS effectively line speed so TASS won't have much to do. One estimate puts the number of curves for which a Pendolino will have to brake from 125mile/h at around the 30 mark
While the Class 390 Pendolini are being built with the wiring for TASS in place, someone will have to supply and install those balises.
Railtrack initially volunteered to do the job, then realised it wasn't covered by the PUG 2 contract so switched to damage limitation mode.
Not to mince words, it is in Railtrack's interests for Virgin to be Pendolinoless in June 2002. Why? Because if Virgin hasn't got the trains to run anyway it doesn't matter if bits of the WCML are a building site or being hand signalled.
Hence the big game of bluff over the timetable. And as you can read below, events are throwing up more work to be done, particularly in the signalling sector, including TPWS.
Such is the political importance of TPWS, that Railtrack suggested, with a straight face, that Virgin might like to wait until 2005 before starting to tilt, running the Pendolini as Virgin Verticale in the interim, giving TPWS installation priority.
When Virgin demurred it was told that it was responsible for providing the TASS balises for its trains. At a four way meeting (Virgin, two train builders and Alstom Signalling) in September it was agreed that Virgin Trains would project manage the installation with Alstom Signalling providing the hardware and coding the balises.
My gung ho chums down the road in Borehamwood reckon it is doable. The project involves 560 balises in total, 70 to keep schtumm and switch out tilt, 280 to notify EPS and the rest for passenger comfort, for example where transition curves are a bit short.