Rail signalling at risk from space weather

Examining two routes - the Preston to Lancaster section of the West Coast Main Line, and the Glasgow to Edinburgh line – the research modelled the effect of geomagnetically induced currents (GICs) caused by powerful solar storms. It was found that GICs flowed through the track circuits of AC electrified lines powered with overhead cables, potentially switching rail signals from red to green and vice versa. The work is published in Space Weather.

“Crucially, our research suggests that space weather is able to flip a signal in either direction, turning a red signal green or a green signal red,” said Lancaster University physics PhD researcher Cameron Patterson. “This is obviously very significant from a safety perspective.

“By building a computer model of the signalling track circuits using realistic specifications for the various components of the system, we found that space weather events capable of triggering faults in these track circuits are expected in the UK every few decades.”

According to the researchers, there are more than 50,000 signalling track circuits in the UK where the signal is controlled by an electrical circuit between the rails. Previous research from the team investigated what is known in the industry as ‘right side’ failures, where the signal is switched from green to red.

While ‘right side’ failures can of course cause issues, they are also a fail-safe scenario whereby rail traffic is likely to come to a standstill. ‘Wrong side’ failures, however, where a red signal turns green, are potentially much more dangerous. The latest Lancaster research shows ‘wrong side’ failures could occur at a lower geoelectric field strength than for ‘right side” failures, meaning weaker geomagnetic storms could more easily trigger the more dangerous of the two potential signal failures. For the two lines studied, it was estimated that, ‘wrong side’ failures could occur due to a solar storm with a frequency of about one or two decades.

“Our research shows that space weather poses a serious, if relatively rare, risk to the rail signalling system, which could cause delays or even have more critical, safety implications,” said Patterson.  “This natural hazard needs to be taken seriously. By their nature, high-impact, low-frequency events are hard to plan for, but ignoring them is rarely the best way forward.”