Ghosts of the past

There seems little doubt that global navigation satellite systems can play a role in building a more effective rail network, as Andy Lee explains.

It’s good to see the rail industry looking forward and not back.

This week’s meeting of minds in London between the railways and the satellite positioning technology community made a welcome change from the activities more usually associated with the rail sector — namely shutting the stable door after the horse has bolted or desperately trying to make up lost ground.

Whatever the technical obstacles to the use of satellite positioning on the railway system — and they are significant, especially in safety-critical applications — there seems little doubt that global navigation satellite systems (GNSS) can play a role in building a more effective network.

GNSS presents opportunities for the railways at many levels, from in-train entertainment options for passengers, to ultra-precise location of track faults and automated safety systems to help remove signal or driver error.

But a question that occurred more than once during discussion of the potential of GNSS on the railways was ‘who’s going to make it happen?’

Building an industry-standard GNSS system that could meet the needs of rolling stock manufacturers, train operating companies, Network Rail, safety bodies, the government and the passengers would test the mettle of industries with a far better record of moving forward together than the UK’s railways.

And even as it looks to the future, the industry is still trying to come to terms with the legacy of its past. GNSS data, from GPS for example, is all about providing positional information to within a few centimetres accuracy — or better.

In the light of this, it was interesting to hear a representative of Network Rail outline his admirable struggle to provide a framework for the future for the rail industry’s own 150-year-old system of linear referencing.

This defines a given position on the network by nothing more fancy than how far along the line it is,calculated by reference to a series of mileposts placed alongside the line.

So a maintenance gang might be told to go to a fault two miles and 107 yds along a particular stretch of track.

Beautiful in its simplicity, you may think, except get this — the mileposts are frequently not a mile apart. Over the years their accuracy has fallen victim to changes in the length of the railway as curves are straightened out.

Maintenance crews move them from time to time, and put them back in the wrong place.

The result? Two miles 107 yds may, or may not be, the distance of the fault along the track. But that is the way the industry works, so any centimetre-accurate GPS readings will have to take account of it.

There, in a nutshell, you have the story of the UK’s railways. For every step into the 21st century there’s a 19th century problem to be sorted out.

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