By Paul Rincon
BBC News science reporter
The rail industry is investigating the use of satellite navigation technology to improve Britain's rail safety.
Sat-nav could deliver real benefits for rail customers, say experts
Dynamic traffic management of railways using sat-nav would improve efficiency and safety, say proponents of the idea.
The BBC understands that an IT company has already conducted a successful eight-month trial using GPS on trains in the south of England.
Key industry figures have been meeting to discuss whether sat-nav could be used widely on the UK's rail network.
Satellite navigation data could, in theory, feed back in real time the positions of every train and item of rolling stock on the network to an accuracy of metres, or even centimetres.
It could also tell controllers whether trains are running to timetable, and which services are running.
Martyn Thomas, representing the UK's Rail Safety and Standards Board at the talks, said it was possible satellite navigation could deliver benefits to rail travellers, providing professional standards were met.
"I think there's general acceptance that the less infrastructure equipment you have and the more intelligence you can place on the train, the better your railway will be," he said.
IT firm SciSys conducted the recent satellite navigation trial with a national rail operator in southern England.
The system is said to have performed better than expected, coping well with, for example, obstacles in the landscape and nearby electrified tube lines, which can interfere with the signal.
To operate Global Positioning System (GPS) technology, the train needs to be able to see the sky to maintain a signal with the satellite. So train tunnels pose a particular challenge.
A sat-nav system on the railways might use Europe's Galileo
"GPS on its own is not a safety critical system for the rail environment. We're going to need to augment it with terrestrial sensors," said Dr David Park, head of the Institute of Engineering, Surveying and Space Geodesy at Nottingham University.
One option might be to place pseudolites - satellites on the ground - along train routes. Another might be to fit trains with inertial navigation systems using accelerometers and gyroscopes.
A number of devastating crashes over the last 10 years have pushed rail safety to the top of the national agenda.
"We're going to have far more information about where trains are and where they are in relation to each other with satellite navigation," said Dr Park.
"With the current block signalling system a train might be anywhere within a kilometre. We'll be able to know, for example, whether a train has accidentally stopped."
Satellite navigation on the UK railways could feasibly use either the US GPS or Europe's Galileo system, which is expected to be up and running by 2008.
The cost of operating a satellite navigation system on the trains would by low, say experts, but the cost of installing it very high.
"Persuading people to finance such a change is probably as complex as the technology," Mr Thomas explained.
"You've got people who own the rolling stock, people who own the infrastructure and people who operate the trains. You can't change control systems on the train without considering implications for control facilities at the trackside."
The issues were discussed on Tuesday at a one-day conference Positioning By Satellite in the Railways of Britain, organised by government-sponsored collaboration Pinpoint Faraday.