'Buckle' in... Britain's hottest day on record brought the nation's transport infrastructure to a halt.
As @Stockton_Boy eloquently puts it:
Mmm, why when other countries cope ok?
Why when other countries cope indeed.
The UK rail network is often a contentious topic to broach with the general public. As soon as delays or cancellations impact a certain line, Twitter is overrun by fuming commuters and holiday-makers who aim their barbed comments at any social media intern who is brave enough to listen.
So, here I am to explain why our trains go (figuratively but also sometimes literally) off the rails when the big lamp in the sky goes full sicko mode.
First, a quick science lesson. When things get hot or cold, they can expand or contract. Railways are exposed to the elements, meaning that the components (rails, overhead wires, and the trains themselves) are susceptible to expansion and contraction throughout the year. This gets worse during extreme weather, such as the July heatwave.
What do railway companies do about this?
Most railway networks 'stress' their rails, wherein the rail is physically or thermally manipulated at a certain mean temperature. The idea here is that the rail will be fine within a certain level of deviation from that mean temperature. Rails in the UK are pre-stressed to 27°C by Network Rail, who are in charge of looking after all of our railway infrastructure.
It's when conditions get abnormally hot or cold that things go awry.
To make matters more complicated, the surface temperature of a rail is often far warmer than the temperature of the surrounding air - in some cases, a rail can be 20°C warmer or more.
Rails tend to expand longitudinally (along the rail) by about 1cm per °C per km. That means that, for an air temperature of 40°C, you can expect a rail temperature of up to 60°C, resulting in an expansion of over 30cm per km.
These high temperatures then cause buckling, where the rails warp out of position, leaving the railway impassible. The risk of severe buckling is increased when trains run over the hot rails at high speeds, as the forces that the trains generate at higher speeds are more likely to have a negative impact on the rails below. This is why speed restrictions are imposed in both extreme heat and cold.
Why not pre-stress to higher temperatures, then?
Unfortunately, this would increase the risk of broken rails in the winter (where the opposite of buckling occurs, and the rails crack due to excessive contraction). If our climate fluctuated less throughout the year, our rail network would be less susceptible to this type of failure.
Why don't we change how we build railways, then?
For the moment, it doesn't make sense to massively overhaul our network to accommodate for these extreme temperatures, as they're currently a rarity in the UK, though this may change if humanity doesn't get it's act together.
Plus, our railway network is one of the oldest in the world, meaning that introducing modern technology to our infrastructure would come at a great financial cost, not to mention the countless weekends of engineering work that it would entail. And, unsurprisingly, Twitter hates engineering work. It hates replacement buses, at least.
How come other countries in Europe cope just fine in hot conditions?
They don't. And it's not just the hot mediterranean countries that experience these issues. In fact, Network Rail uses some of the same short-term measures to prevent rail buckling as nations like Italy and Austria, such as painting the rails white to keep them as cool as possible.
Additionally, countries further south tend to have longer summers, meaning the conditions are more predictable, and the rails can be pre-stressed accordingly.
If you've made it this far, well done! You can share this valuable knowledge with your peers next time someone starts a debate about our railways being rubbish. Because they're not rubbish. They're trying as hard as they can. And that poor customer engagement officer on Twitter isn't to blame for it.
Thanks to Network Rail for sharing this thread today (Tue 19 Jul) explaining some of the key challenges that they face as our national railway infrastructure manager.
There's also this Reuters article which says much the same thing but uses different pictures.