What solar storms could do to train services
Charged particles are repeatedly hurled towards the earth from the sun. This can lead to a disturbance of the earth's magnetic field. But it can also affect train signaling systems, as a recent study shows.
Even minor solar storms, which can be expected every ten to twenty years, can turn railroad signals from red to green - which poses the risk of collisions. This has been shown by British and Canadian scientists using computer simulations. The reason for this is track vacancy detection systems, which are part of a circuit that includes the rails. Geomagnetically induced currents could affect this circuit as a result of a solar storm. Many similar systems in Germany work on the same principle. The study by a group led by Cameron Patterson from Lancaster University in Lancaster has been published in the journal "Space Weather".
"Our research shows that space weather poses a serious, albeit relatively rare, risk to the rail signaling system that could lead to delays or even have more serious safety implications," Patterson is quoted as saying in a statement from his university. Although there are already modern track vacancy detection systems in the UK that are less sensitive to disturbances in the Earth's magnetic field caused by a solar storm, older, vulnerable systems are still widespread, the authors of the study write.
Train creates a short circuit via the tracks
For these older track vacancy detection systems, the railroad lines are divided into so-called track blocks of around half a kilometer to two kilometers in length. A relay is located at the beginning of a block (viewed in the direction of travel) on the lines examined, which receives power from a source at the end of the block. If there is no train in the track block, the circuit is closed via the rails and the relay receives power; in this case the signal shows "green", free track. If there is a train on the track, its wheels and axles cause a short circuit: the relay receives no current and the signal jumps to "red".
Patterson and colleagues specifically investigated the British railroad lines between Lancaster and Preston and between Glasgow and Edinburgh. They recreated the track vacancy detection systems on these sections of track in a computer model and then simulated currents of the kind that can be triggered by high-energy particles from the sun in the Earth's magnetic field. They determined that individual track vacancy detection systems on the Lancaster-Preston line can be disturbed by an electrical voltage of just 1.1 volts per kilometer, causing the track signal to change from red to green. On the Glasgow-Edinburgh line, even one volt per kilometer is sufficient.
Such electrical voltages can be caused by solar storms, which, according to long-term statistics, can be expected once every one or two decades. Solar storms, which occur on average once a century, can even generate four volts per kilometer of electrical voltage. Numerous signals can then be disturbed in succession, not just individual ones. For their simulations, however, the researchers assumed that the trains on the line are always about to leave a track block. The longer the distance between the relay and the last axle of the last wagon, the greater the risk of signal interference.
Space weather forecasts could help
The risk of signal disruption also depends on how many trains are on the line. "In the future, space weather forecasts could be used to make decisions about restricting rail operations when an extreme event is expected, just as meteorological forecasts currently do," emphasizes Jim Wild from Lancaster University, a co-author of the study. The next step would be to test the computer simulations with experiments, the scientists write.
According to the researchers, an example of space weather switching railroad signals occurred in Sweden in July 1982. A signal changed from green to red and back to green during a geomagnetic storm, even though there was no train on the line or other fault conditions were present. The authors of the study also refer to earlier statistical analyses that had identified an increase in the number of unexplained signal malfunctions during periods of high geomagnetic activity.
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Source: www.ntv.de
