Train tracks struggle in the heat – here’s how they stay cool

UK rail service has been hit by widespread train delays and high levels of cancellations during the heat wave. The entire east coast line between Edinburgh and London was closed for hours on July 20 due to the heat.

So why is the heat wave wreaking so much havoc on train lines? Like most construction materials, the steel, from which rails are made, expands as the air temperature rises. When this movement is limited by the anchor, which holds the rail and sleeper (the rectangular rail supports) in place, internal stresses build up and the compression buckles or bends the rail.

This buckling can cause a long piece of steel, such as a steel rail, to bend or bend slightly. Trains cannot run on tracks with nodes. In the United States, deformations caused by the sun have caused more than 2,100 train derailments in the past 40 years, or about 50 derailments per year.

When the air temperature reaches 30°C (86°F), the rails in the sun can reach 50°C (122°F). In the UK, a temporary speed restriction is imposed when the rails reach this temperature as trains apply less pressure to the rails as they slow down. Some railroad maintenance crews paint the tracks white to cool them in the summer. According to Network Rail, this can reduce rail temperature by 5°C to 10°C. Network Rail workers started paint the train several days before the July heat wave.

Modern rail systems are getting better at keeping the tracks in place. Most tracks are made up of long pieces of rail that are stretched and welded together, which helps hold them in place. This reduces the risk of buckling. When a track is made up of short rails bolted together, Network Rail leaves small gaps between each to allow for expansion in hot weather.

Electric trains are often powered by overhead cables, which can also be damaged in hot weather. Heat can cause wires to expand and sag. Too much sag will break the overhead line equipment. A pulley system keeps the overhead wires taut and can compensate for sag.

How other nations are coping

As temperatures reach unprecedented levels, even Spain’s train lines, which usually withstand the heat well, are warping and services are cancelled.

Continuous solder rails, which are used as standard worldwide, including the UK, are optimized to operate around a given ‘unconstrained temperature’ (SFT). The higher this temperature, the more the rails can heat up without burning.

In the UK, the SFT is 27°C (80.6°F), the traditional average railway temperature in summer. In the United States, the standard values ​​vary between 35°C (95°F) and 43°C (110°F).

If the UK SFT were higher, the railways could operate in warmer weather because the rails would not expand as much at higher temperatures. But if the rails are rated for too high an SFT, they won’t be able to cope with the colder temperatures they experience in the winter. This would create enormous stresses and the rails could shear their anchorage.

Railways in some countries are able to cope with such temperature variations by using strong concrete slabs to contain the higher forces created. But slab tracks cost about four times as much to install as standard ballasted tracks.

Climate change means that railways in many countries will more often reach temperatures for which they were not designed, threatening public transport on a scale never seen before. We have just seen the highest temperature on record in the UK at 40.3°C (104.54°F), well above the previous daily record of 38.7°C (101.66°F) in 2019.

During the construction of HS2, the new high-speed railway being built between London, Manchester and Leeds, bridges and overhead cables were fitted with sensors to collect weather data, including the temperature of the air. This data will be used to create the digital twins of HS2, enabling a new type of maintenance capable of predicting high temperatures and other types of disruptive weather conditions.

A digital twin is a digital representation of the railway network. This would allow engineers to simulate future scenarios for the UK rail network and predict what might happen if high temperatures are forecast, and be able to take preventative action in advance. This could be a way to avoid some of the huge cancellations seen during the recent UK heatwave.

Kangkang Tang, lecturer in civil and environmental engineering, Brunel University London

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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