Modelling Data for a Rainy Day: How PRIMA is Revolutionising Rail Safety

Featured story12 February 2025

With climate change gathering momentum heavy rain is set to happen more often and can lead to flooding, earthwork failures, derailments, and damaged infrastructure. In 2023, bad weather caused around 15,000 hours of delays. Our new tool, PRIMA, can help.

We’ve developed a new data-led decision-support tool for Network Rail called PRIMA. It can reduce the delay hours caused by heavy rain. PRIMA stands for ‘proportionate risk response when implementing mitigating speeds to assets.’ It uses data modelling techniques and analytics to give rail operators more insight into the safety risks associated with rain. They can then use this intelligence to plan how to respond in a proportionate way.

Weighing Different Kinds of Risk

Before now, blanket speed restrictions (BSRs) have often been used to keep trains running safely. BSRs curb the safety risk to passengers and crew travelling through areas affected by rain. But in a complex system, they can have knock-on effects causing additional, different risks to those same trains or elsewhere on the network.

Trains running outside their normal patterns risk passing through signals at danger. Delayed trains can lead to overcrowded platforms. Managing speed restrictions can also put extra pressure on signalling staff and route managers.

In short, a slower railway isn’t necessarily a safer one.

Looking for a Solution

In 2020, a derailment at Carmont was caused by debris washed on to the track by heavy rain. Since then, 40 mph BSRs have become much more common. Network Rail has used 40 mph BSRs once rainfall passed a set threshold. The same threshold was used all over the network, without accounting for local conditions.

This led Network Rail to wonder whether a more nuanced response was possible. So we investigated how to optimise BSRs to reduce train accident safety risk. We looked at:

characterising the relationships between climate events
climate-vulnerable lineside assets
train movements
balancing the immediate safety risk to trains in rain-affected areas and the knock-on risks elsewhere on the network.

We combined our expert rail safety knowledge and data insights capability, and our risk modelling experts worked alongside geotechnical specialists.

The result of this work is PRIMA.

What is PRIMA?

PRIMA is a decision-support tool for rail operators drawing up speed plans for routes, section by section. It gives them a view of whole-system risk for each section. PRIMA weighs the immediate risk of an accident with the knock-on risks to the wider network. It then suggests running speeds for each section of track. It also produces a cost benefit analysis of speed restriction options.

Network Rail can combine this information with their local knowledge to produce speed plans for operating route sections. For example, frequent changes of speed over short sections might be difficult to communicate and less ‘driveable’ in practice.

The result is speed restrictions that are proportionate to the risk that bad weather causes.

Modelling All the Relevant Data

PRIMA’s model is based on rainfall data and the condition of earthworks, embankments, and cuttings in each route section. It uses this data to calculate the risk of a derailment, given the known state of earthworks and the amount and rate of forecast rainfall. PRIMA then balances immediate safety risk against other risks caused by imposing speed restrictions. This all comes together with suggested speeds that can inform the decision-making process.

And one more benefit – PRIMA is a cloud-based tool. Its fully designed dashboard makes information and suggestions for speed restrictions easy to access.

Trialling the New Tool

PRIMA has been trialled on two routes in the North West and Central region, and four routes in Scotland. These routes cover a range of different speeds and conditions.

The North West and Central trial drew on local knowledge from asset management staff to refine the model, based on their insights about specific earthworks. The results look positive.

Next Steps

In 2025, we will work with Network Rail to roll out a version of PRIMA in new areas.
We are updating the tool to model the risk of falling trees caused by high winds.
Following a successful presentation at UIC, we will investigate whether PRIMA could be applied internationally.