Risk – How To Model It, How To Manage It

Featured story

In a three article series, we explore where our unique approach to risk and decision-making supports a better, safer railway.

In this first piece, RSSB’s Chris Harrison explains what risk is, and how the railway tries to understand it better with the Safety Risk Model.

The word ‘risk’ conjures many different perceptions. Taking a risk can be seen as good or bad, depending on the consequences. For example, investing in a new start-up company that may result in a return of millions of pounds is seen as something positive. Whereas the risk associated with health or crime has more negative connotations. Risk aversion is often equated to lacking confidence in new ideas or innovation. The word entrepreneur literally means risk-taker.

When we talk about risk we are usually thinking about the likelihood of something bad happening. In a safety-critical industry like rail, understanding this is vital.

Railways are one of the safest forms of transport, but there are hundreds of different hazards that all have their own level of risk. Lying in wait, these hazards present various levels of potential for harm to the workforce, to passengers, and to the wider public. But if there is so much risk present, how come railways are so safe?

The answer lies in all of the excellent safety management practice undertaken by the industry. This is supported by risk analysis and modelling.

Imagine you throw a six-sided dice numbered one to six. The probability you will throw an even number is one in two (50% chance). So, if we pretend that an even number is a hazard that you need to manage or avoid, you know it’s going to happen on average half of the time you throw the dice. Other less frequent hazards might mean throwing a bigger dice, potentially one with hundreds of sides! The point is that different events occur with different frequencies, and we can make estimates and model how likely they are to happen.

In reality, there are a lot of different potential hazards with all sorts of probabilities—many of them very low. Estimating the likelihood that they will happen is largely done using historical data, bolstered by a lot more research and data where needed. The railway needs a model, a framework, that can take into account lots of different numbers, probabilities, combinations, and situations to understand how likely each of the things are that can go wrong.

There are also lots of different consequences that may occur when something does. An event could have a low probability, but come with high levels of harm if it does happen. Other events may happen more often but have a less severe impact. The railway uses a common unit fatalities and weighted injuries (FWI) to enable comparison between all the different types of injuries that can occur.

However, just because you know more about the hazards, the risk they pose and how this might arise, does not remove all of the uncertainty around them. If possible, controls and mitigations would be put in place to eliminate the risk completely. However, this is not always possible and you can’t reduce risk to zero. Nor can you spend infinite amounts of money fixing every single risk. Managing risk takes effort, resource, and time. So, you need to know where the risk is exactly and how bad it is. Only with that information can you be more efficient, and target problems effectively.

The Safety Risk Model (SRM) has been helping people in GB rail take sound, risk-based decisions for over two decades. It describes and quantifies the underlying level of risk arising from the operation and maintenance of the railway. It helps decision makers set safety priorities and analyse safety-related costs and benefits. So they can confidently and demonstrably meet legal requirements and wider business objectives. As far as we’re aware it’s the most comprehensive and well-used rail risk model in the world.

The SRM feeds a whole range of other tools and resources that help Britain’s railways get a better understanding of risk. The SRM also provides the stimulus for cross-industry work. It informs safety strategy, for example in Leading Health and Safety on Britain’s Railways. It’s a starting point for lots of the R&D and Standards work that identifies efficiencies and unlocks innovation, without compromising safety. A lot of time and money is saved with the SRM.

Over the last year, we’ve overhauled the SRM. We’ve introduced significant improvements while retaining key features that make it so powerful and widely used. The biggest change is that the model now estimates risk locally as well as nationally, based on the characteristics of the railway, the trains that run on it, and the people who use it.

If you’re an RSSB member, there’s a whole section on our website on the SRM which takes you through exactly what it is, what’s changing, and how you can get the most out of it.

Another tool that the SRM enables is the Precursor Indicator Model (PIM). This looks specifically at the things that could cause a train accident to happen. The beauty of the PIM is that, while it uses the long term risk data from the SRM, it provides a dynamic, up-to-date view of risk trends every four weeks, by combining it with real-time performance data. Outputs are presented at a national and regional level in the PIM dashboard so users can explore different aspects of train accident risk.

If you’re an RSSB member, there’s another section on our website on the PIM, which takes you through it, as well as the interactive dashboards.

These tools are well worth a look. If you want to find out more about the work we do in this space, member or non-member, please do get in touch with us via the Customer Portal link below.

On 7 July we will be publishing the Annual Health and Safety Report for Britain’s railways. This is a key output from the Leading Health and Safety on Britain’s Railways strategy. Look out for our videos and publications.

More information

Haven’t found what you’re looking for?
Get in touch with our expert for more information.