Historical evidence reveals that space weather has affected rail networks in the past via disturbances of the signalling system. Although many of the documented rail-system anomalies linked to space weather occurred at high latitudes, there is an increasing awareness that the risk to grounded infrastructure posed by naturally occurring geomagnetically induced currents (GIC) is present and remains a threat to mid- and low-latitude regions (such as the UK) as severe and extreme space weather events push geomagnetic disturbance equatorwards.
However, it remains unclear if GIC interference in rail track circuits would always lead to right-side failure (a failure condition in railway signalling that results in a safe state) or a wrong- side failure, thereby creating a more significant safety risk. It is also recognised that the rail sector is not as advanced as other infrastructure sectors, such as electricity transmission or aviation, and that signalling misoperations or anomalies caused by space weather are unlikely to be recognised or recorded as such.
This project aims to explore the vulnerability of railway signalling due to a significant, but not widely considered, natural hazard. The objectives are:
1. Understand the relative importance of environmental factors (such as the intensity of the geoelectric field and the electrical properties of underlying geology) and the characteristics of rail infrastructure (such as the length of the signalling rail sections, their orientation relative to the geomagnetic disturbance and the electrical properties of equipment) in determining the risk of right- and wrong-side failures. We will construct a track circuit model of the UK rail network that will enable us to estimate the intensity of geomagnetically induced currents in the UK national rail network and assess the impact of these currents on signalling systems under disturbance levels of varying severity, from typical to the realistic worse-case scenario (based upon historic data). This will be the first model of its kind anywhere in the world.
2. Enable an accurate estimation of the geoelectric fields that drive GIC through the Earth’s surface and grounded infrastructure in the UK. This will be achieved by combining existing magnetotelluric survey datasets and a new set of measurements specifically targeted at sites close to the rail network. By comparing variations in magnetic and geoelectric fields that have been measured simultaneously, a relationship or transfer function will be computed at each site that allows readily available magnetic field measurements to be converted into estimates of the geoelectric field. These will allow us to apply magnetic field data spanning four decades to the rail network model and assess where and when anomalies are likely to occur. We shall also implement a prototype nowcasting tool by driving the track circuit model with real-time magnetic field data to present a live dashboard of signalling anomaly likelihood.
3. Internationalise our technique. Due to different geology, geography, rail system architectures and operational approaches, the vulnerability of rail to space weather varies between countries. However, the underlying methodology is applicable in other countries. Having developed our technique in the UK context, we shall apply it to the North American setting, leveraging the expertise of the Project Partner, based at Natural Resources Canada.
4. Inform researchers, industry stakeholders and policy makers. Beyond academia (see Beneficiaries section) we shall use the applicants’ existing activities within the UK Space Environment Impacts Experts Group that advises Government on the Space Environment and its potential impact on UK infrastructure and business, to feed our finding into government and policy-makers. We have also established a Project Advisory Group of industry, regulatory and policy experts to act as critical friends and a direct route into key stakeholders.
Space weather encompasses a range of environmental phenomena, ultimately driven by solar activity. The emission of solar energy and material directed towards Earth can drive electromagnetic disturbances at the planet’s surface. Under normal levels of solar activity, the impact of space weather is minimal. However, natural variations in solar activity can drive periods of severe (typically on decadal timescales) and extreme (once every few hundred years) space weather during which the intensity of these phenomena can increase by many orders of magnitude. Rapid, high-amplitude geomagnetic variations during space weather storms induce geoelectric fields in the electrically conductive subsurface of the Earth. The imbalance in the geoelectric field between different regions causes Geomagnetically Induced Currents (GIC) to flow in conducting structures grounded to the Earth. Space weather thus presents an environmental risk to some of the critical hardware, infrastructure and services underpinning our society and economy. The risk of space weather is recognised by its inclusion in the UK National Risk Register for Civil Emergencies.
Railways were among the first modern infrastructure to be impacted by space weather due their reliance on telegraph technology for signalling purposes. It was reported in an 1871 issue of Nature that the interference due to a geomagnetic storm delayed trains in Exeter, and the astronomer Walter Maunder, reported interference with railway signalling equipment during the geomagnetic storm of November 1882. The storm of May 1921 had such an extensive impact on the operation on railway operations in New York State that it has been dubbed the “New York Railroad storm”. Modern signalling has moved away from telegraph-based systems, but contemporary technologies are not immune from GIC. Track circuits are one of the main systems used to detect trains along a section of railway line and prevent other train from entering that section. They rely upon an electrical circuit in which the train’s axles close a current loop between the rails but are vulnerable to interference from stray currents induced in the rails. There is recent evidence of anomalies in such signalling systems that coincided with the occurrence of geomagnetic-storm conditions in Swedish and Russian rail operations. Signalling systems reported false blockages (right-side failure) in sectors where no trains were present and statistical analyses of anomaly data indicate that the occurrence and duration of these anomalies showed a 5-7 times higher probability of occurrence during strong geomagnetic storms. These impacts may not be limited to infrastructure at high latitudes. Indeed, there is an increasing awareness from parallel research to understand the risks posed to electricity transmission grids that the GIC risk is a threat to mid- and low-latitude regions since severe and extreme space weather events push geomagnetic disturbance equatorwards. However, the risks to rail systems remain uncertain. For example, it is unclear how likely GIC are to induce wrong-side (i.e. safety critical) failures in such systems and we have yet to experience the impact of a reasonable worst-case scenario, such as the 1859 superstorm known as the “Carrington Event”, on modern rail systems.
In this project, we shall undertake experimental and modelling work to comprehensively explore the space weather risk to rail signalling for the first time. This will include measurements that will enable us to assess the geoelectric field imposed upon the ground in the UK under any observed geomagnetic conditions. We will also build a state-of-the-art computer model of the rail network in the UK that will enable us to evaluate (i) the geomagnetic environmental factors and (ii) the characteristics of the network relevant to signalling misoperations. The results will be important for other space weather researchers, rail operators and policy makers.
