Did you already have sweat patches 15cm in diameter by 9 this morning? Have you pledged allegiance to Satan, if only he’ll let you enter hell after your death, rather than introducing it to the Northern line as an art installation? Does the thought of getting on the bus home this afternoon leave you screaming like the goat in Taylor Swift’s “I Knew You Were Trouble”?

If so, you may be a long-suffering commuter currently enduring what we in the UK call “a heatwave”, or what our friends in Australia call “Tuesday”.

Sure, it’s hot. But why should a little bit of heat so often lead to transport chaos? Why do trains get cancelled because of the heat, when they have air conditioning installed on them?

Here are just a few reasons why everything goes up in a puff of smoke at the first hint of sun.

Because wires

The heatwave of the early bit of last summer was, for those with a short memory, pretty intense. Wednesday 1 July was the hottest July day ever recorded in the UK, with temperatures around London coming in at 36.7°C (98°F).

As a result, Greater Anglia was forced to implement speed restrictions on its rail services in Essex. That led to severe delays and cancellations, as trains weren’t able to run to their usual schedule.

The problem? The tracks in the areas around Shenfield and Southend, both in Essex, are dominated by very old overhead wires which supply the electricity for the line. When these heat up, they start to sag: that means they can get in the way of the train, or even break altogether.

Whilst a project to replace 1950s-vintage tech across the Greater Anglia network was underway, the service still suffered as the veteran wires struggled with the high-30s heat.

Because tar is not for walking on

The launch of Disneyland in Anaheim, California, was an event on a national scale. Ronald Reagan, then a celebrated actor and later to become a sort-of celebrated president, was part of the official opening ceremony, and viewing figures for the event’s televised coverage reached around 70m.

The weather of that July day in 1955 had other plans. As temperatures climbed to over 100°F (around 38°C), the brand new asphalt on Main Street, USA, started to melt. According to accounts of the event, women’s high heels became stuck in what essentially turned into sticky tar.

Asphalt in Lyon starts to melt in a heatwave in 2006. Image: Getty.

Because when the sun suns a lot it gets really sunny

You might think that January is the one time of the year where the pounding intensity of the sun wouldn’t get in your way of a day’s commute. You’d be wrong. In January of this year, Southeastern services in South East London saw long delays and cancellations because of – yes, really – “strong sunlight”.

With an awareness of the seeming ridiculousness of the situation, a Southeastern spokesman said: “We know that sometimes it seems that if it is not leaves on the line or snow on the track then it is some other weather issue. But actually the glare this morning made it impossible for some drivers to see the full length of their train in their mirrors before leaving mirrors.”

Whilst this has an air of “no, honestly, Mum, I don’t know how the china got broken”, it seems the issue was genuinely a problem in two different ways. Firstly, getting out of the train every time you stop, to see if everyone has got onto the train safely before you shut the doors, is obviously a right faff. Trains get delayed, and eventually some trains – like, the literal vehicles – will be unable get to a place in time and services get cancelled.

Secondly, drivers couldn’t see their dispatch monitors clearly because of the glare. That in turn means they can’t read signals effectively, and thus don’t quite know when to start or stop, and so go for stop because it’s safer.

Because delays are better than deaths

Great Western Railway (GWR) has today cancelled all its direct trains between London Paddington and Oxford. Why? So that they can run other bits of their network more slowly. Passengers trying to go through will have to change at Didcot Parkway (as a local: I’m so, so, sorry) for the time being.

Whilst this all seems an unnecessary hassle just to run a few trains more slowly, it does make sense. James Davis from GWR said: “With temperatures in London set to exceed 30°C, the effect can bring the temperature of the rails to over 50°C, and we have been asked by Network Rail to drive more slowly as a result”. At that point, physics kicks in: as the metal rails get hotter, they naturally expand, which causes extreme compression of the joints. As the pressure builds up eventually something gives, and the track can buckle.

Although this only happens very rarely, the pressure is increased by heavy trains full of passengers and goods hurtling along at break-neck speed. And if a bit of track does buckle, then that’s it: any train that goes over it will derail, and – crash. That’s what probably happened in Sydney in 2003, when nine people died and 39 were injured. It might be annoying to be delayed, but I’d imagine most of us would rather be a bit miffed than dead.

Because if it’s hot on the surface it can be really, really hot underground

As we reported back in 2015, some parts of the London Underground can reach staggering temperatures in the heat. While “sub-surface lines” – those closer to the surface such as the Circle, Hammersmith & City, and Metropolitan lines – are generally cooler, and run through larger tunnels meaning the trains have space for air-conditioning, the deep lines have no such luck.

Parts of the underground can reach temperatures beyond the limit at which it is legal to transport cattle, and the mercury on the Central Line last night was well into the mid-thirties. Following much the same logic as with the GWR lines to the West, speed restrictions have been imposed today on several underground lines.

On a more pleasant note, though, TfL are also handing out 250,000 bottles of water today to commuters in the hope that it’ll keep them cool and encourage better travelling habits. So that’s nice.

Old-fashioned modes of transport can be rather easier to keep cool. Vienna, 2003. Image: AFP/Getty.

Because things will literally melt

In August of last year, a British holidaymaker in Italy spotted something rather unusual. In a car park by the beach in the town of Caorle, near Venice, a car literally started to melt.

In temperatures of 37°C, the lights, wing mirrors, and window fittings of a Renault Megane started dripping onto the road. John Westbrooke, from Kent, said; “We just couldn’t believe what we were seeing. Even bits of the bumper were melted and the wing mirrors were starting to buckle.

“I guess the moral of the story is don’t trust French cars.”

Something something, Brexit.