The Hatfield disaster three years ago not only shook confidence in the UK’s railways but also revealed the level of ignorance about the condition of rail infrastructure.
An emergency programme of ultrasound testing was needed to find how widespread similar defects were. It revealed a huge maintenance backlog, requiring months of speed restrictions on large parts of the network.
But if Hatfield sowed the seeds of Railtrack’s eventual demise and its replacement by Network Rail, it also had a galvanising effect on the approach to infrastructure monitoring, with the result that Network Rail is now among world leaders in its approach.
One example is the introduction of the world’s first service train that can measure track geometry – a vital area because it carries the greatest risk of derailment.
‘Hatfield reminded everybody that monitoring the engineering performance of the railway was very important,’ said Keith Madelin, director of Rail Research UK. ‘There were periods when Railtrack lost sight of the fact that it was managing an engineered product. You ignore that at your peril.’
After Hatfield, Railtrack set up an engineering department for the first time. Andrew McNaughton was appointed its first chief engineer.
‘We started looking not at what the railway was doing, but what it should do,’ said McNaughton. This process has intensified under his direction at Network Rail.
‘The UK’s railways are 160 years old and for most of that time maintenance has depended on a lot of people looking at the infrastructure and making judgements, with a high degree of subjectivity and variability,’ he said.
The central aim of the new method was to use technology to collect objective information where cost-effective, McNaughton explained, and then to useit to decide what work to do and when – in other words, replacing a reactive approach with a predictive one.
Two and a half years on, the plan is bearing fruit. A range of technologies are being introduced across the network following successful trials.
‘The strategy is now to inspect frequently so we will be looking not for defects but trends,’ said McNaughton.
Variability and fallibility in human inspections will be removed. The expense of maintenance will be lower because it will have been planned to take place without disrupting services, not under pressure in an emergency.
‘The technology doesn’t replace people,’ said McNaughton. ‘Machines will do repetitive objective measurement – which is what they do well.’ Skilled people will still be deciding what remedial work is needed and when.
One of the most exciting developments, according to McNaughton, is the track geometry measuring train.
Equipment to automatically measure track geometry has been around for 30 years or so, but originally it took up a whole coach.
Now, instrumentation specialist Imagemap of the US has miniaturised the equipment so it fits on the bogie of a passenger train. Laser probes measure the position of the track in 3D and the data is downloaded via the internet at the end of a run. Software filters it, looking for changes, and alerts engineers to emerging defects.
The system has been in place on the Chiltern line for the past few months and has been hugely beneficial, said McNaughton. Along the line are some weak embankments made of ash, which dries out and can subside. ‘We have been able to watch the deterioration day by day and intervene to maintain safety, avoiding the need for expensive earthworks monitoring equipment.’
The Imagemap technology, which costs about £1m for each unit, is now being introduced across the network.
The second key area of monitoring is the condition of components such as sleepers, clips and so on. Network Rail and French rail operator SNCF have been undertaking trials of video technology developed for military satellites by French firm Cybernetix. A train-mounted camera records continuous video images of the track and can be ‘trained’ to recognise defects. It is capable of spotting a piece of crushed ballast on the track, a crack 5mm long in a sleeper or a missing clip while travelling at 180mph.The results are uploaded to Network Rail’s maintenance system and stills are presented to an engineer to decide what the defect is and what action to take. An information centre is currently being equipped in Derby to filter the data before sending it to engineers locally.
The most visible sign of the predictive approach is the New Measuring Train, a converted High Speed Train painted bright yellow. Because it can travel at 125mph, it can run between scheduled trains without disrupting the timetable. At present it covers the main line network on a two week cycle.
Two of its five coaches contain the monitoring equipment and another has been fitted out as a conference centre to train line engineers and supervisors.
The initial configuration of the NMT carries the Cybernetix technology and a number of other devices aboard Network Rail’s existing Track Recording Coach and AEA Technology’s TrackLab coach. The Imagemap 3000 system works alongside the previous measuring system to calibrate the new with the old.
TrackLab provides a rotating laser capable of measuring what is known in railway parlance as ‘the six foot gauge’ – the separation between adjacent tracks – at 10cm intervals. Video recording of the wheel/rail interface is used to check that the wheel is rolling correctly on the railhead and not hitting the side – this leads to gauge corner cracking, the cause of the Hatfield disaster. Again, the data can be filtered to highlight problem areas and allow grinding of the railhead, to restore its correct profile, to be programmed.
AEA’s Vampire technology is being used: this contains a complete library, in software, of the suspension characteristics of all rolling stock. It combines this with the geometry data to check for derailment risks.
Recording of noise is being experimented with, to detect rattling of loose components.
By next April, the NMT should be in its final form. Two new coaches will contain the latest technology, including a laser system by Germany’s Fraunhofer Institute to measure the geometry of overhead electric power lines. The force on the pantograph, or current-collector, will also be measured, as this gives an indication of its condition.
By modifying an existing train instead of building a new one it has been possible to get the NMT into operation within 18 months at a cost of around £10m, about a fifth that of measuring trains being built elsewhere in the world. NMT will become the flagship of a fleet, with the existing recording coach and TrackLab forming another train to work on secondary routes. There will also be a 100mph Southern Measuring Train, with most of the capabilities of the NMT, for work on the Southern region. Here manoeuvrability takes priority over speed.
With the Imagemap system in place, it will be possible to measure track geometry weekly, to video plain line once a month and to monitor overhead electrification every six months.
In the past, companies developing rail technology have complained of the difficulty of getting it accepted. The spare NMT coaches will allow Network Rail to offer space to manufacturers to use it as a test bed. ‘It’s a completely open approach,’ said McNaughton, ‘so we’ll be the first to get new ideas.’ Interest has already been expressed by companies around the world.
One thing the new technology will not detect is missing nuts on points, which led to the Potter’s Bar disaster in 2002. McNaughton said; ‘I’d rather use humans for points.’ And because hours of inspecting plain track will be eliminated engineers will have time to do this. Other aspects of points, such as motors, need to be inspected so the bolts can be done at the same time.
McNaughton summed up the new approach: ‘The change from reactive to predictive maintenance is the biggest change in 150 years. If we can give companies trend information early, they can plan maintenance and resources properly and do a better job. We’ll have a safer railway, with fewer interruptions and greater punctuality.’
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