For those in the signalling or rolling stock professions, it is all too easy to think of track maintenance as an old-fashioned undertaking, devoid of modern technology and dependent on technicians with jacks, spanners and shovels. However, this perception is totally wrong. Civil engineering track maintenance equipment has developed into the most sophisticated across all of the engineering disciplines.
The advancement does not stop there and new methods of automating the inspection of track are evolving all the time. the rail engineer was recently invited to ride on Network Rail’s New Measurement Train (NMT) from London to Bedford in order to see the Plain Line Pattern Recognition (PLPR) technology which is now being introduced as a means of monitoring the condition of the track without the need for patrolling and visual inspection in the time-honoured way.
Setting the Scene
Robin Gisby, Network Rail’s managing director of network operations, explained the mounting challenges that the company faces in the track maintenance arena. Firstly, there is the pressure on cost. Each maintenance delivery unit employs about 240 direct and 80 indirect staff. Getting more value from these units is important and using them for renewal work, such as switch and crossing replacement in the remoter areas, is one initiative. However, this can distort the revenue and capital budget allocations.
Secondly, using a risk-based approach to get more work done in the busy high-traffic areas and less in rural locations focuses the resources into where they are needed most.
Then there is the squeeze on track access times as the pressure to extend the hours of train services is adversely affecting the time for doing work. This leads to a need to maximise the available time within a possession, especially where isolations are needed in third-rail territory.
Automating these procedures would have a very real benefit. The safety of track workers, and avoiding the need to have them out and about when trains are running, should be part of an improved productivity initiative. Finally, the quest for more mechanisation to do things in a more efficient way with fewer manual tasks is all part of the ongoing plan.
Inspection at speed
Trains to monitor various aspects of track condition have been around for many years. These have tended to be regionalised in deployment and only capable of specific tasks. The NMT, a converted HST with five coaches including testing and analysis vehicles which is capable of 125 mph, has been the test bed for seeing whether all the necessary monitoring can be undertaken by a single train.
The NMT is 115 metres long and weighs 337 tonnes. Whilst track condition measurement is the primary task, the train is additionally equipped for OLE monitoring via on board pantographs such that wire wear, height and stagger can be monitored. Knowing the train position is essential to meaningful measurement and this is achieved by a combination of on board GPS readers, odometry tachometers from a starting reference point, an inertial unit so that the systems know when the train has changed tracks and an underlying map, called the Network Rail Infrastructure Model (NRIM). This gives positional information to a general accuracy of 2 metres and guaranteed accuracy of 16 metres.
Getting time-consuming labour out of track inspection is the primary focus, and this is done both by the examination of the actual condition of track components and by the measurement of track geometry. Initially, PLPR is concentrating on continuous welded rail, but ongoing work will use the same techniques for assessing switches and crossings as well as jointed track.
So successful have the results been that four additional trains are now being formed. One of these, for the third-rail area in the South East, will be formed by two Class 73 electro-diesels sandwiching three Mk 2 coaches and a Mk 1 generator vehicle giving a maximum operating speed of 90mph. The other three trains, capable of 95mph, will each be hauled by a Class 57 diesel together with a similar train formation and a Driving Van Trailer (DVT). All five trains will be in service by early 2013.
The intention is to survey all operational lines at least once every year, with main lines being covered every two weeks. The NMT, because of its higher speed, will concentrate on the West Coast, East Coast and Great Western main lines, with the three Class 57 trains doing all other lines outside the South East. All this will mean measuring 250,000 miles of track every year, involving day-long operation and needing 1,800 work shifts. The NMT is programmed to do 5,000 miles per week, with the other four trains doing 10,000 miles each week collectively. Twelve separate asset condition streams are monitored, each with their own recording platform
Examining the rail
Traditional inspection of rail condition consumes 1.3 million man hours of work each year. Using the NMT and the other trains for PLPR will remove 520,000 hours of this, which above all else will be a significant safety benefit. Four lasers, seven linescan and a number of thermal imaging cameras are mounted on the underside of the train. These high-speed cameras are synchronised and capable of taking photographs at the phenomenal rate of 70,000 pictures per second. At 125mph, this gives a picture of the rail every 0.8mm.
The digital images are stored on solid-state disks accumulating five terabytes of data on every run. The disk data is then copied to on-board computers known as the ‘processing factory’, a task which takes eight hours to accomplish. Part of the process is to condense the data down into manageable elements, and this task alone takes about 75 minutes to produce results. Finally, the data is compressed down to about 10 Mbytes for sending out to section managers so they can plan remedial works. Using the new 4G radio network for sending the data in the future could save significant time.
Data will be kept for four runs over the same piece of track so as to build up a record for that section. General data will be kept for three years. An information management system is being built which will be capable of comparing one run’s outputs with previous ones.
The on-board video surveillance system has been designed by Omnicom, a York-based company set up in 1990 and employing 45 people, some of them ex-BR with knowledge of monitoring requirements. The firm has been successful in developing video techniques for inspection and surveying including real-time positioning systems for both the rail and road sectors. Network Rail is also using Omnicom’s expertise in areas such as asset identification and signal sighting as well as this application for track monitoring.
The downward pointing cameras look at the inner, outer and top sections of the rail for aberrations including rail burn and other heat-related defects. Part of the system is the OmniVision viewer, a software based application that creates and presents any potential defects, known as ‘candidates’, for validation by an on-train inspector (OTI). Typically, 15 candidates are found every mile, of which about four in each mile are classified as true defects. 32 OTIs will be deployed across the five trains.
Measuring track geometry
It is not just the rail condition that is important. Knowing the overall alignment of the track, as well as its position in relation to all other structures and assets, is another element of the measurement routine. The laser-scanner monitoring equipment works to a route setting map that uses structures such as stations, bridges, and tunnels as reference points to measure inter-track spacing (the six foot) and ballast shoulder heights. The movement of the train is detected by gyros, accelerometers and transducers with cameras looking at the floor of the train and all surrounding objects.
Clearly the position of the train relative to the infrastructure is critical. If any maintenance is carried out which involves changing bogie springs and similar components which could affect the running height of the train, a re-calibration exercise is needed before a further measurement run can be undertaken.
Three main potential track geometry defects can be detected:
• Twist – rail height one to the other over a given distance;
• Cyclic Top – imperfections that create bounce in certain types of rolling stock, which if bad enough can cause vehicles to derail;
• Gauge – separation between the two rails.
To be effective, the latest measurements must be compared with previous runs so as to detect change. All faults are given GPS co-ordinates. If a serious defect is found, the OTI will be alerted and the train will be stopped. This in itself gives a measure of protection as succeeding trains will be restricted on that section of line. The local maintenance unit will be informed so that urgent remedial action can be taken. Fortunately, this happens very rarely, itself an indication of the improved maintenance regime.
On board the train, VDU screens show all the measurements taking place in real time. An additional forward-facing video camera, mounted on the HST power car nose, displays the track ahead.
The NMT and its forthcoming sister trains are a big leap forward in the task of track maintenance. Going forward under the banner of project ORBIS (Offering Rail Better Information Services), the rail measurement system is only one of a number of trackside tasks that can be made more efficient by automation. For example, a new ultrasonic test train will shortly be coming on stream to measure structure gauge for bridges, tunnels and, eventually platform height and clearance.
The overall objective is to have a data collection service that has a record of all assets, including how they fit together in relationship to each other, which will generate accurate and timely defect information. This will be used to produce degradation models that can give guidance on where problems will occur in the future and to understand better the interaction between trains and infrastructure.
All of which will be derived from thorough track inspections, carried out at 125 miles per hour and without anyone having to venture out on track.