How the Whole System Risk Model stops rail overcompensating for extreme weather events
The safety risks posed by earthworks subjected to extreme levels of rainfall are significant. Waterlogged earthworks can collapse suddenly with little or no warning, and if there’s a train on the line adjacent to earthworks when they collapse, derailments and even fatalities can occur. As we see increased changes in our climate and the probability of extreme rainfall increase, it is necessary for rail to have robust procedures to respond.
However, the complexity of the network means that a single response applied everywhere in an identical way is not the answer. Although Network Rail initially implemented a blanket restriction on train speeds in areas where earthwork failures had occurred or were likely to occur, doing so could cause additional and unintended problems. This raised the possibility of rail inadvertently overcompensating for extreme rainfall and potential or actual earthworks failures. Despite being a highly safety-conscious industry, overcompensating for extreme weather events is not the answer.
RSSB had a two-pronged solution to this challenge: first, carry out research, and secondly, develop a model to help operations.
The research found that blanket speed restrictions in response to high intensity rainfall events are justified. Relevant characteristics to include in the calculation of blanket speed restrictions include imposed speed, affected lines, a weather severity threshold, and the monitoring period before the speed restriction is removed. However, rail operators also need to consider characteristics of the local network because the model found that the effects of the blanket speed restriction were strongly affected by features of the local network. This means that applying blanket speed restrictions to the whole network is probably too cautious and should be avoided. Future versions will include other types of extreme weather events as well.
So how can RSSB members apply the Whole System Risk Model to their operations? There are two different outputs depending on your role. The report gives an overview of the research and possible paths for implementation. This is most likely to be useful for engineering and operations teams, risk managers, and risk practitioners. However, the preliminary user guide is more detailed. It is targeted at the engineering and operational teams of infrastructure managers and their need to understand the correct inputs as well as the correct interpretation of outputs.
Whatever your role, RSSB is keen to learn from early use of the model in the field. So download the report or preliminary user guide and give us your feedback.
