Space storms could switch signals and cause serious train accidents

A number of electrical systems in the railways of many countries, including the UK, are vulnerable to space weather. In the worst case, a red signal could be turned green, potentially causing a deadly train crash, says Cameron Patterson at Lancaster University in the UK.

“You could have disruptions to signalling systems, which are crucial to railway safety,” he says. “We have to prepare for these things now, and getting that message across, I think, is really important.”

The sun is constantly blasting out charged particles, as well as light. This solar wind is what causes auroras. Sometimes, the sun emits more material than usual in what’s known as a solar storm, which can affect Earth’s magnetic field.

The main danger is to satellites, but solar storms can also affect electrical systems on the ground because any change to a magnetic field can induce unexpected currents, including in railway tracks.

That’s a problem because many railway systems rely on direct currents running through sections of track to detect the presence or absence of trains, says Patterson. When a train passes through, it changes the amount of current flowing.

“When you introduce geomagnetically induced currents into the mix, that can cause all kinds of anomalies, turning signals that should be green red, or the reverse,” Cameron told a recent meeting of the European Geosciences Union in Vienna, Austria. “You’ve got to remember these trains are going at very high speeds. If they don’t have advance warning, it might be too late to slow down.”

Patterson knows of only one clear case of signals being affected during a solar storm, in Sweden in July 1982. “They saw signals switching and linked it to geomagnetically induced currents flowing through that track section,” says Cameron.

He suspects there have been many more cases like this, but that it seldom occurs to engineers that space weather might be to blame. By the time engineers reach the scene, the storm is usually over and they find nothing wrong, he says. In Russia, research has found correlations between solar storms and signalling anomalies.

While red signals turning green is the biggest danger, green signals turning red can also cause major disruption. If trains get stuck and electrical systems fail, passengers may leave the train, putting themselves in danger, says Patterson.

The risk is thankfully low. Solar storms strong enough to cause this kind of issue only happen around once every 30 years, he says. “But a 1-in-100-year event might very well happen next month.” Very large storms could cause widespread blackouts, causing major disruption.

Some countries use a different signalling system in which magnetic sensors count the number of passing train wheels, says Patterson. It isn’t clear if these systems are vulnerable to geomagnetically induced currents.

A number of other train systems are also vulnerable to disruption from solar storms, he says, including transformers connected to overhead electric lines, the systems used to tilt trains as they round curves at high speed, radio communications and the satellite navigation systems used for purposes such as detecting the precise location of a train.

Patterson is now collaborating with Network Rail, the Rail Safety Standards Board and engineering companies in the UK to help them make systems more resilient. It was hard to get those conversations started, he says, but they are taking it seriously.

Magnus Wik at the Swedish Institute of Space Physics agrees that signalling anomalies due to solar storms may be going undetected. “They may experience a short disturbance and then it is back to normal, and they don’t know what caused it and [have] no evidence of it,” he says.

Wik says Sweden modified its railway system in the 1950s after signals turned from red to green during geomagnetic storms in the 1930s. In the 1982 incident, it turned from green to red, he says, which is less serious.

“The Swedish Transport Administration probably don’t know if this can occur again or if it has happened multiple times,” he says. “We have discussed a possible study to check for past geomagnetic disturbances and compare with error logs, but this is not official.”