The impact of heat on the railway network

Source: RTM Jun/Jul 16

Emma Ferranti, Lee Chapman, David Jaroszweski and Andrew Quinn from the University of Birmingham, alongside Network Rail’s Caroline Lowe and Steve McCulloch, analyse heat-related failures on south east England’s railway network.

Network Rail owns and operates Britain’s rail infrastructure, incorporating over 20,000 miles of track, more than 2,500 railway stations, and a wide variety of signalling, telecommunication, and overhead line equipment. 

Heat can cause numerous problems for the railway infrastructure, and affects the different asset types in different ways. For example, temperatures above 30°C are often associated with track-buckling incidents. Research at the University of Birmingham has shown that on a warm day and in direct sunlight, the tracks can be 20°C warmer than the ambient temperature, and this, combined with the extra energy of a passing train, can cause buckling of the track. 

To reduce the chance of buckling, Network Rail slows down the average speed of trains along vulnerable sections of track on days when ambient temperature is predicted to rise above critical threshold temperatures. Higher temperatures can also lead to thermal expansion of the overhead lines that supply electricity to trains via a pantograph. If the overhead lines expand, their tension reduces, which can lead to excessive line sag. This can cause the pantograph to disconnect. 

Heat can also impact signalling and communications assets that may be stored in manned signal boxes, remote relay and signalling rooms, or in lineside location cases. Those assets which are located in direct sunlight are most vulnerable to overheating, especially the equipment inside location cases, which can be much hotter on the inside than the ambient temperature is on the outside. Heat-related problems can even occur at relatively mild temperatures such as 15°C, with the number of incidents increasing significantly above 26°C.

Figure 1

Delays and disruption 

Heat-related faults and heat-related emergency speed restrictions cause delays and disruption for the tens of thousands of customers who use the railway network on a daily basis, and also incur notable financial cost to Network Rail in the form of compensation payments to the TOCs that use the infrastructure. Heat is therefore a significant concern for Network Rail and without targeted adaption the costs associated with heat-related delays are projected to increase as high-temperatures and heatwaves become increasingly common under a future warmer climate. 


The Summersense project at the University of Birmingham (2014-16) investigated the impact of heat on the railway infrastructure located in south east England. This region is warmer and drier than the rest of the UK and more likely to have heat-related incidents than other parts of the UK. In particular, the Summersense project invested the idea of ‘failure-harvesting’. 

The research team hypothesised that on the first warm days of the year, those assets that were most susceptible to heat would fail, and then be repaired or replaced with new assets that were more resilient to heat.  On the next slightly warmer day, other weak or vulnerable assets may fail under the higher temperatures before being repaired or replaced with new assets that were more resilient to heat. Consequently, as the summer season progresses, the infrastructure should become increasingly resilient to heat as the failures are harvested on early warm days. 

The researchers tested the hypothesis using Network Rail incident data from 2006 to 2013 and the results are shown in the table above. There is a clear reduction in the number of heat-related incidents for both track and signalling assets in August, despite this month being equivalently hot or indeed hotter than some of the preceding months. This suggests that the failures are harvested early in the summer season as hypothesised. The research also highlighted the impact that heat can have on signalling assets – these accounted for 53% of heat-related incidents whereas track incidents accounted for only 20%. 

Heat-risk management 

The research has implications for heat-risk management by Network Rail. Understanding that more heat-related incidents occur early in the year could help target routine maintenance, particularly of signalling assets which account for the majority of heat-related incidents. There is also scope for Network Rail to change its heat-risk management procedures in the future. 

If it can be conclusively proven that the infrastructure has become resilient to heat before the end of the summer season, the number of heat-speed restrictions applied in August could be reduced. This dynamic heat-risk management would save Network Rail money, and reduce the delays and disruption for customers.

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