British train system is getting another excuse for delays - solar storms

Space weather can wreak havoc on electronic systems, but while most folks focus on protecting datacenters or the power grid, a group of UK researchers are warning that relatively mild solar storms could bork train signaling systems. 

Boffins at Lancaster University wrote in a recently published paper that the potential for a geomagnetically induced current (GIC) caused by a solar flare or coronal mass ejection – like the one that pelted Earth earlier this month – could cause "right side" errors as well as their more hazardous counterparts, "wrong side" errors, in train signals. 

While both involve electronically controlled track signals displaying inappropriately, right side errors mean a train signal is erroneously reporting that a track is occupied and unsafe for another engine. Wrong side errors are when a track signal that should be red – indicating an oncoming train is headed down the track and may not be visible – flips to green, suggesting it's safe to travel the track.  

"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. This is obviously very significant from a safety perspective," argued Cameron Patterson, a Lancaster Uni physics PhD student and lead author on the paper. 

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Per the paper, Patterson and Professor Jim Wild constructed digital models of two AC-electrified train routes equipped with DC track circuits – from Preston to Lancaster on the West Coast Main Line and from Glasgow to Edinburgh. The team explained that circuit relays are designed to be de-energized when a train axle passes them – causing the lights to flip from green to red and indicate the track isn't clear. 

Patterson and Wild slowly increased the values of a modeled electrical field to see how much it took to trigger a wrong side failure, arriving at comparatively low thresholds for errors in both eastward and westward travel. Indeed the thresholds for both were far smaller than an electrical field observed from solar storms in 1982 that caused disruption on Swedish trains.

A concerningly common possibility

The likelihood that a wrong side failure happens in a particular track circuit block is largely dependent on the position of a train in a particular block, between the power source and the relay. Still, the team noted that the threshold when compared to the sort of space weather that hits impacts Earth means such errors could be more common than first thought.

"We found that space weather events capable of triggering faults in these track circuits are expected in the UK every few decades," Patterson noted. The pair observed in their paper that wrong side errors appeared to require less magnetic field strength to trigger than right side errors – meaning there's a serious safety risk on the tracks that has been largely ignored. 

"Other industries such as aviation, electricity generation and transmission, and the space sector are considering the risks to their operations, and exploring how these might be mitigated," argued Wild. "It's important that the rail sector is included in this planning."

Once-in-a-century solar weather events could have an even greater impact, the pair noted. When using a previous estimate of the field strength for a 1-in-100 year geoelectric field, multiple blocks experienced failures – both wrong- and right-sided. Then again, if a really big solar storm hits, we'll have bigger problems.

According to Lancaster University, there are more than 50,000 signaling track circuits in the UK. As more tracks are electrified, the risks only rise. 

"In future, we could see space weather forecasting being used [to] make decisions about limiting railway operations if an extreme event is expected – just as meteorological forecasts are used currently," predicted Wild. ®