Temperatures in south-east England are set to hit 31C today, causing a strange problem for the UK's railways: bending rails. But how can a warm summer day potentially bring the UK's trains to a standstill?
Rails are made of steel which expands as it heats up. If trains go too fast they risk buckling the track. While the air temperature might be 31C, temperatures on tracks can exceed 50C during heatwaves.
Just a few hours of above-average heat is enough to cause problems. Today's hot weather has caused First Great Western to impose speed restrictions and alter some services in the Thames Valley until 8pm.
Blanket speed restrictions, which prevent trains from slowing down and speeding up excessively, are the best way to prevent buckling in hot conditions. Both the heat and the train passing over a rail can cause it to buckle, which is why in some instances trains may be cancelled altogether.
To stop this from happening hydraulic machines are used to artificially stretch rails as they are placed. This stretching means that even if the rails heat up they won't expand, but once temperatures go beyond 30C overheating becomes an issue.
There's also a limit to how much a rail can be stretched -- take it too far and you risk rails cracking during cold winters. How much a rail is stretched is therefore a careful balancing act.
The problem can also be exacerbated by the poor condition of a rail line. If the gravel used to lay rails and sleepers has fallen away tracks tend to wobble, which can worsen the impact of buckling. Newer lines, laid with better fastenings and sensors to detect potential problems, are less prone to buckling.
While the amount of expansion is relatively minor, when expanded to mile upon mile of welded steel it becomes significant. As modern tracks are welded together into continuous lines to create a smoother ride this small expansion is amplified. On straight tracks the buckle is typically "S" shaped, on corners you normally get a "C" shaped buckle.
High-quality ballast, sensors and regular monitoring of rail conditions during both extreme hot and cold weather should all ensure a hassle-free ride for passengers, but hot weather continues to cause problems for the UK's railways.
This article was originally published by WIRED UK
