REPLACING railway signalling equipment with satellite navigation systems could slash the cost of maintaining the network and provide a financial lifeline for lightly used rural railways by cutting their costs.
A nine-month trial using a train on the UK rail network, reported at a conference in London last week, showed that the satnav technology could successfully replace trackside signals. It reliably displayed signalling information inside the driver鈥檚 cab, while equipment in the signal control room showed the position of the train.
鈥淔ears of interference or blocked signals proved groundless. The only blind spots were tunnels鈥�
Advertisement
Maintaining conventional signalling systems can eat up as about 10 per cent of the cost of running a railway. The new system has been geared to help operators of lightly used railways, says Gareth Close of satellite consultancy SciSys, based in Chippenham, Wiltshire, in the UK.
Railway signalling systems divide the track up into short sections, each guarded by a signal that remains at red while the section ahead is occupied. These trackside signals are expensive to maintain and vulnerable to vandalism. In some countries it is not uncommon for people to steal lengths of cable and sell them for the copper they contain.
The trial, which was backed by the British National Space Centre, was the first on a publicly used railway. It followed trials of a similar system on a test track in Belgium last year. The test train carried a GPS receiver capable of determining its position to within 4 metres. Using a link to the Iridium satellite communications network, or a mobile phone network if the satellite link failed, the system then broadcast the train鈥檚 position to signal boxes.
Software feeds this position data into the railway鈥檚 existing signalling system, which keeps track of all the trains over a broad area of the network. This works out whether to display a danger signal or the all-clear on the panel in the train cab that takes the place of the trackside signals.
While GPS navigation is used extensively in aircraft and ships, railways were expected to pose more problems. Deep cuttings could block the train鈥檚 view of the GPS satellite鈥檚 signal, and electrified sections could interfere with the signal itself or with the cellphone link. The trial proved these fears groundless, and the only blind spots were tunnels. 鈥淲e knew where the train was to within 4 metres of accuracy,鈥� Close says. 鈥淲e were able to follow it right up to the buffers of [London鈥檚] Paddington station, even under the glass canopy on the train shed.鈥�
But Peter Ladkin, a safety analyst at the University of Bielefeld in Germany, warns that the system may be unreliable. 鈥淚t is easy to jam GPS, inadvertently or deliberately.鈥�
