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2009 Issues Archive
9 September 2009
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Guiding track
It seems an odd idea but GPS and other satellite navigation systems are essential parts of the modern train, writes
Ben Sampson
It’s hard to find a more linear style of travel than rail. Trains go from A to B and back again. One would assume if a train driver didn’t know his location, he is a) going to find his career very challenging, and b) putting a lot of train and passengers in danger.
It’s initially surprising then that the global positioning system (GPS) and other satellite navigation aids are already used on the railways. Even more surprising is that the extension of their use is a serious research consideration – one in which the European Union has invested millions and that train manufacturers are rapidly pursuing. What possible use could satellite navigation have for a train driver?
It turns out quite a lot, once you overcome the preconception of everything GPS being related to car satnav or stranded mountaineers. Martyn Thomas, control command and signalling engineer for the Rail Safety and Standards Board (RSSB), says: “GPS has been in use on the railways for at least 15 years. Most trains built since 2000 are fitted with GPS for one purpose or another. It was first introduced to relate performance recording and monitoring of passenger numbers with location. Passenger information and door controls are more recent introductions.”
There are other minor existing applications, for example in safety for trackside workers. Researchers are looking at other applications, including automatic control of freight trains in mines and depots, collision avoidance systems, and creating interoperability between countries with different signalling systems. There are various applications where satellite positioning for trains is useful, says Thomas, and could give cost benefits over other technologies in terms of reliability, dependability and safety.
The big event for satellite applications on the railways is the European satellite navigation system Galileo, due to be operational in 2013. Galileo should afford greater accuracy and reliability, increasing the technology’s suitability for rail. But with other signalling technologies such as ERTMS and in-cab signalling being introduced Europe-wide is an eye in the sky really necessary?
“Satellite technology fits in very well with other new signalling technology,” says Thomas. “Some investigations have been undertaken for a European research project called Grail and a Network Rail project. Benefits have been identified and further work is required on achieving the safety requirements.”
Up to speed:
The Galileo satellite (top) is expected to improve reliability and and accuracy on the railways. But signals will still be necessary
Last month Siemens’ railway division announced it would build a test track capable of simulating the signal that Galileo will produce at its Wegberg-Wildenrath test facility in Germany. The project, Railgate, is being conducted with Aachen University and will use eight signal generators, pseudolites, mounted on 50m transmission masts to transmit Galileo signals. Trains fitted with receiver devices will run on a 28km stretch of track to test applications such as automatic marshalling or train tracking.
The tracks are in a wooded area and have peripheral existing infrastructure, such as depots. This will be an advantage, explains Martin Baier, group leader of rail in the Institute of Automatic Control at Aachen University, because it will allow researchers to study the shadowing effects from terrain such as forests. “There is a lot of work to do and there are a lot of problems to solve with the design and construction of the testbed,” says Baier. “For use of Galileo in general in the rail sector, the most challenging problem is intelligent integration of the satellite data in safety applications. Research has to determine which combination of sensors has to be used in which manner to get the best positional accuracy at the minimum cost.”
Tunnels and cuttings, urban areas, forests – there are lots of areas where satellite systems could and will fail. This is the main reason, admits Baier, that satellite navigation is unlikely to ever be the sole positioning system on the railways, but it can be an “important element of the next step in signalling technology”.
Thomas adds: “Some applications don’t need continuous coverage and there are techniques to extend coverage. Some form of data fusion is usually required. Satellite navigation is not necessarily the dominant location sensor but is useful as one means to control errors in other sensors.”
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© PE Publishing, 9 September 2009
