Why don’t rails get hot in Europe? The truth is they do.
However, in countries typically hotter than ours, rails are stressed to withstand higher temperatures.
Hot weather can cause a great deal of disruption to the railway so Britain’s rails are pre-stressed to help them resist high temperatures. Our rails have a stress-free temperature of 27 degrees – the UK mean summer rail temperature. Other countries choose different temperatures depending on their climate.
When the air temperature reaches 30 degrees, the temperature on the rail can actually be up to 20 degrees higher. More than three-quarters of track on the network today is modern on concrete sleepers.
For some of our track, such high temperatures are more than our track is designed to cope with, however. The problem is that when steel rails get hot, they expand, which can cause a buckled rail.
Some countries regularly have extremes in temperature that affect their railway. They may adjust their rails between summer and winter, or have other measures in place to manage the effects over the long term.
In Britain, the variations in short-term weather and long-term climate mean that it is neither practical nor cost effective to implement these measures permanently on the British rail network.
We do all we can, however, to ensure services continue to run safely and smoothly at times of extreme weather.
The steel rail on a railway track is a very long piece of metal that can expand or contract significantly in the summer and winter. This generates forces that try to push and pull the railway out of shape. The mass of the sleepers and ballast are designed to contain these forces and prevent the track from buckling.
In some countries the forces generated by temperature variation cannot be contained by sleepers and ballast, and a solid concrete slab is used to contain the higher forces. Slab tracks costs approximately four times as much to install as standard ballasted track.
The movement of trains also generates forces in the track. The higher the speed, the greater the force of a train. When heat expansion forces are high, trains deliberately slow down to reduce the additional forces they apply to the railway. The need to prevent problems also means there will be fewer trains, but this is better than causing a bigger problem and being unable to run any services.
The overhead line system (pictured) expands in the same way as the track. Within a certain limit of expansion, the tension in the wires is automatically adjusted. You can see the adjustment weights at the lineside as part of the overhead line system.
Beyond the limit of adjustment, the wires sag, causing a risk that a passing train could pull them down. Slower trains reduce this risk.
Why don’t we replace all our rails with ones stressed for higher temperatures?
Temperatures have been rising in the UK, particularly in East Anglia, so this may seem like the obvious solution. The problem is that if we stressed Britain’s rails to the same degree as those in very hot countries, there would be the risk of increased tension on the rails in the winter.
What is Network Rail doing?
The hot weather forecast this week means Network Rail has activated its ‘extreme weather action teams’ (EWATs) to ensure passenger safety and that we keep our railway running as reliably as possible.
We are monitoring track-side temperatures and will, if necessary, introduce temporary speed restrictions at the hottest times of the day to keep trains running, albeit more slowly than usual.
Read about how we deal with extreme heat on our buckled rail page.