Return to Archive -by date - by topic -Archive 2002.
More accurate infrastructure knowledge shows TPWS will be more effective than predicted – TPWS+ will further enhance protection
During the Southall and Ladbroke Grove inquiries there was a concerted effort by the bereaved and survivors groups to rubbish the Train Protection & Warning System as cheap, nasty and infective. They argued that it would provide protection against only 60-70% of potential collisions and would not stop trains travelling at over 74mile/h within the standard 200 yard overlap.
In their parallel joint inquiry into train protection systems, Professor Uff and Lord Cullen quoted a number of analyses of the effectiveness of TPWS in preventing fatalities. In 1994, British Rail Research estimated that it would save 68% of fatalities caused by SPADs. This estimate was ‘open to substantial criticism', commented the two QCs.
Subsequent studies by various consultants gave effectiveness levels ranging from a low of 55% to a high of 66%. Then in January 2000, in his report on train protection, Sir David Davies quoted a figure of 65% effectiveness compared with ATP, but noted that this was ‘likely to be a low estimate'. Sharp chap, Sir Den, now Chairman of Railway Safety.
Uff and Cullen rounded this down to 60%, which they thought was justified given ‘the inherent and unavoidable uncertainty in the data under consideration'.
Meanwhile, under the lash of the Rail Regulator, Railtrack had been building up its infrastructure knowledge. And this knowledge includes the actual length of overlaps.
Simultaneously, there has been a fitment programme to provide what is termed ‘Enhanced Emergency Braking'on disc-braked trains. This upgrades brake systems to give an emergency braking rate of 12%g. Don't worry about the number, just bear in mind that for signal spacing purposes old tread braked stock is good for 7%g, a disc braked IC125 brakes at 9%g below 100mile/h and modern multiple units with Westinghouse's latest brakes and wheel slide protection can manage 12% in the wet.
In March I gave the keynote address to the 2002 National SPAD Conference attended by 200 senior managers, operators and engineers. Naturally I stayed on for the day to improve my knowledge and one of the items that emerged was a new estimate of the benefits of TPWS
According to these latest figures, TPWS-A (the plain vanilla version) should account for 81% of SPAD risks. This improvement reflects site surveys where the location of collision points has been found to be beyond the standard 200 yard overlap.
At the Conference, Chris Leah, Director Safety & Environment Railtrack plc, reported that TPWS-A installation was ‘just about on schedule', with 43% of signals and 48% of trains fitted but, ‘struggling' towards Railtrack's accelerated end-1992 completion target. Legally, TPWS-A to be operation across the network by the end of 2003.
Of course, TPWS, of any flavour, will not reduce the total number of SPADs significantly, rather it will convert Cat 3-8 serious events to Cat 1-2. It is a palliative not a prophylactic.
However, not only is TPWS a more effective palliative than first thought, it is more versatile than the ATP-at–any-price lobby would have us believe. In particular, if you want to provide protection at higher speeds TPWS+ is now ready to roll out.
In effect TPWS-A knows how fast a train can approach a red signal and still stop safely. If you are going faster than that when you pass the Over Speed Sensor (OSS), TPWS-A applies the brakes and, depending on the excess speed, stops the train somewhere in the overlap.
TPWS+ does the same thing, but it adds a second OSS , typically 800metres in rear of the red signal. Depending on the location of the OSS , trains running at up to 100mile/h could be brought safely to a halt.
Pilot TPWS+ installations have been under evaluation at Hitchin and Doncaster and GNER Production Director Richard McClean told the SPAD Conference that they were proving a success. As an operator of high speed trains, he wanted to know how TPWS+ could be taken forward. He urged that implementation should start before the TPWS-A design, manufacture and installation teams were disbanded.
In reply Railtrack's Chief of Engineering Andrew McNaughton agreed that TPWS+ was ready to be installed, but he was worried that it might be ‘larded on as a universal solution.' He proposed a programme of selective fitment, following analysis of junctions where TPWS+ would reduce risk significantly.
Rod Muttram, Head of Railway Safety added that TPWS+ was in the ‘workstream' of the ERTMS Programme Board, which would consider its integration into the ‘front end' of ERTMS installation.
All very magisterial, but very old railway. However one beneficial side effect of Railtrack's Administration has been a perceptible swing of power and initiative to the Zones and Regions. And the Zones and Regions are close to their customers.
So next to speak was Railtrack Eastern Region Director Robin Gisby who warned that the decision to install TPWS+ should not be over-analysed – ‘given two coats of looking at' was his phrase. He was supported by Richard McLean who also believed that identifying the locations where TPWS+ would give benefits on GNER routes would be a simple matter.
Indeed, after the conference, a chum in Railway Safety got out his Quail maps for some desk research and reckoned that we are talking of around 150 locations network-wide, mainly flat junctions on high speed lines, where TPWS+ would give obvious benefits.
Which brings us to cost. Sir David Davies estimated the cost of installing TPWS+ at around £70million at the time of the Joint Inquiry. This sounds high (yes I know I don't usually say things like that about signalling) since all the expensive work of interfacing TPWS-A with the signalling interlockings will have already been done.
On average it costs £20,000 per signal to fit TPWS-A. Installing TPWS+ should be cheaper.
There would seem to be two options: either roll out half a mile of cable and connect the extra TPWS+ OSS to the existing TPWS-A interface; or do a quick and dirty link to the signal in rear so that a yellow aspect armed the TPWS+ OSS. Given that TPWS+ is belt and braces and the industry's own initiative, I would not be fussed about whether the additional OSS was fail safe and it could be driven off the signal lamp.
Either way, TPWS+ sounds like a sub £5million project.
So now, this column is the official sponsor of the campaign for selective installation of TPWS+ on the East Coast Main Line. This would benefit both GNER and Virgin Cross Country which will be running Voyagers at 125mile/h. As a first step the two high speed Chris's – Garnett and Green – have confirmed that they both think it is the way to go.
While this column is nothing if not dedicated to the rule of the cold numbers when it comes to safety, I think that unilateral selective installation of TPWS+, would finally take safety off the political agenda.
Already, at least in my view, the industry is winning an increasingly desultory ‘railway safety debate'. Installing TPWS+ to protect the ‘no-brainer' high speed flat junctions with the greatest risk of catastrophic collision might not make sense in terms of value per prevented fatality, but the emotional capital would be huge, to be drawn on the next time the industry has to face the media in the aftermath of an accident.
By the time you read this, the ERTMS Programme Board (EPB) will have presented its report on the implementation of the system. Informed Sources suggest that commonsense has triumphed over the naïve recommendations of Uff/Cullen report on Train Protection systems. In line with the European High Speed Interoperability directive, the EPB recommends that ERTMS, or rather its signalling component the European Train Control System, will be installed on high speed lines as existing signalling is renewed. Likely timescales would see the Great Western Main Line following the West Coast Main Line – with installation completed by 2010, by which time replacement of the East Coast Main Line signalling would be falling due. In depth analysis next month together with a report on the new layout and equipment at Paddington, held over because of the political excitements above
|