Signalling a change

A satellite-based command-and-control system for railway lines could dramatically cut the cost of operating quiet sections of track, according to its developers.

The system, developed by the Locoprol project, uses GPS technology, combined with an onboard digital map of the track, to pinpoint the train’s position with a high degree of accuracy but without the need for a range of expensive additional sensors. It also aims to plug the gaps in GPS coverage of a rail network caused by obstacles such as tunnels and cuttings.

Partners in the EU-backed project include engineering groups Alstom and Honeywell, and French train operator Connex.

According to project co-ordinator Michel Rousseau, existing control systems for busy sections of railway track are uneconomical when transferred to low-density lines — those that only carry one or two trains an hour.

The Locoprol system, which is now ready for roll-out following successful testing, employs a custom-developed positioning algorithm on board the train that uses satellite range signals and converts them into extremely accurate location data.

Rousseau said that the development of the algorithm was important in order to achieve a consistent level of accuracy.

‘GPS signals have a low integrity level,’ he said. ‘We needed to use the algorithm to make the GPS more accurate, and to give exact speed and positioning information to the train’s onboard sub-system.’

The sub-system carries a detailed digital map of the track that includes information on any signals and curves on the line, as well as topographical data. Detailed track information is crucial in allowing the system to calculate a real-time safe interval between itself and other trains on the line.

In the event of losing the signal the system also uses additional in-wheel sensors which act as a back-up positioning system. These communicate with passive trackside ‘balises’ — transponders which currently operate as part of automatic train protection (ATP) systems.

Information is first used by trainborne equipment to operate the ATP functions that keep trains safely separated. It can then also be sent to a trackside control centre to be used in traffic management.

Initial tests in Nice earlier this year concentrated on testing the algorithm in real-life conditions and de-bugging the software. They also looked at integrating the Locoprol project with the future introduction of the European Rail Traffic Management System (ERTMS), and any specifications or difficulties that it might impose.

As the system primarily relies on satellite visibility, Rousseau believes that the introduction of the Galileo satellites — the European alternative to GPS — will mean that in the long-term the technology’s applications will widen.

He said: ‘We believe the technology could eventually be used in medium and even high-density lines.’ The system could be in use within three years, said Rousseau.

Initial applications are likely to be on mining rail networks in South Africa and South America, but it could also be used on quiet passenger lines in western Europe, including the UK, he claimed.