As temperatures rise, the 20,000 miles of steel that make up the UK's rail network expand, curve and buckle, while overhead power lines sag into the path of trains, causing delays and ruining your trip home. With sympathy to commuters sweating on a slow train, there's not much we can do about it.
Record high temperatures this week have forced train operators across the UK to adjust their timetables, with as many as a third of trains cancelled across the southeast, with speed restrictions imposed on those that are running. But such problems aren't limited to the UK. Indeed, railways in France and Germany have also cut services and speeds in response to the European heatwave, while trains in Australia were forced to slow down last summer.
The main threat is buckling rails, when heat causes the steel in tracks to bend and warp. Slower trains cause less stress on rails, so they're less likely to buckle, and slower, less frequent services are better than none at all – though it may not feel that way as you stand sweating on a hot, crawling service.
Rails buckle for an obvious reason: they're made of steel, and metal expands in heat. While steel rails are pre-treated to endure heat stress, there's a limit to their range.
Gareth Dennis, railway engineering consultant, says steel works across a roughly 60-degree temperature operating range, while Network Rail notes that rails can be 20 degrees warmer than air temperature. In order for rails to function in winter temperatures without cracking, the steel in British rails is designed to operate between roughly -10 and 30 degrees without any stress, says Kevin Groves, chief spokesperson for Network Rail, though the rails can handle up to 36 degrees without buckling. "If you live in Saudi Arabia, you just shift your rail up the engineering scale say from +10 to +50, as track has the same engineering range wherever you are," he explains. "You just prepare it based on your typical climate."
That's accomplished via "stressing" steel when it's laid as rails, essentially stretching it out using hydraulics so it doesn't expand or contract within a certain temperature range. "Stressing is an activity that happens when any new track is laid," Groves explains. "If you went up to any rail and decided to cut it, it would ‘ping’ back to its ‘stress free’ length as a track is stretched and welded when laid to enable it to cope with our normal summers."
That preparation helps rails withstand some stress, but the full stress-free temperature range is only in perfect conditions – and plenty of British rail isn't perfect. Some is simply old and in need of replacement, or the ballast materials it's laid on needs maintenance. "Often we haven't renewed these materials for decades," says Dennis. Any bits of track that are complicated, such as junctions where tracks are connected or splits away from each other, will reduce the stress-free range, hence why so many London stations have speed restrictions in place on hot days, adds Dennis.
There's more to help rails than stressing. The buckling risk can also be reduced by improving the materials the track is fixed with or laid onto. Ballast is the bed on which track is laid, and in the UK it's often gravel. The heavier and more solid ballast is, the better the rails can withstand heat. Slab track used in Austria and parts of Japan uses concrete as a base, but it's up to four times as expensive as standard construction. "It's not just about the rails, it's about the track materials as well," Dennis says. There are other techniques to avoid buckling, such as avoiding heat by painting rails white, which Network Rail says can reduce heat by ten degrees.
Read more: The UK's record-breaking year of hot weather in numbers
When temperatures do hit the high thirties, Network Rail sends out Extreme Weather Action Teams, which sounds awesome but is just staff sent out to watch important or worrisome locations, in order to impose speed restrictions and send workers to fix buckled rails. A maximum speed limit of 60mph was imposed across most of the southeast on Thursday, Groves says, with normal speeds between 75mph and up to 125mph. Such efforts have reduced buckling by 83 per cent since 2003, Network Rail notes.
Though Groves didn't couldn't immediately supply figures about how many incidents were recorded last year, a document from University of Oxford researchers suggests 2003 with its summer heatwave was particularly bad for buckling – perhaps why it's chosen as a base line – with 137 incidents, suggesting there's only a couple dozen buckling cases each year now. That's good news, as those 137 buckling incidents cost £2.5 million to fix.
Rails aren't the only issue. Another is power lines; also made from metal, they sag in the heat. One solution is what's known as an auto tension power line. "Rather than a line ending at a fixed point (such as a big post) the line will wrap around some pulleys and then connect to a massive weight stack that keeps the lines constantly under tension and constantly taut," Groves explains. Another problem is the ground beneath tracks, which when hot summer sun dries it out can pit and pothole, removing support for rails. Taku Fujiyama, a senior lecturer at University College London, also points to on-board computers overheating as a source of delays in heatwaves.
Given we're likely to face more extreme weather conditions as the climate emergency worsens, what can be done to improve the British rail network's ability to withstand the impact of heat?
To start, we shouldn't look to the past. Some critics pin the blame for buckling on a shift to new rail laying techniques, notes Dennis. In the UK, rails are joined together in multi-kilometer long pieces called continuous welded rail, rather than laid individually with gaps between them, a system called jointed track, with lengths of steel bolted together.
The latter technique was previously used in the UK back when labour was cheaper and it wasn't too expensive to send workers out to fiddle with 50 to 100 joints per mile, says Dennis. But though that allows some space – a few millimeters between each joint – for rails to expand to help avoid some (but not all) buckling, it also leads to rougher journeys and raises issues with maintenance, and contributed to fatal accidents, including the 1967 incident at Hither Green that killed 50 and another in Elgin that killed a passenger.
So what can be done? Improving maintenance and upgrading rails and ballast seems an obvious answer, but its costly and disruptive to rip up rails that work fine all but a few days of the year, says Dennis. "The number of days a year we have these issues is small, compared to the cost of replacing everything at once." Indeed, countries with extreme temperatures – Dennis pointed to Siberia – keep their trains running by restressing rails as seasons change, an expensive, disruptive process.
That said, alongside improving maintenance of the rail network, Dennis calls for continuing to improve remote monitoring as well as better weather forecasting, as that allows for advanced preparation and more targeted response by Network Rail's engineers. "The ways we get around it is the technological ways to mitigate and manage the risks and consequences, rather than inventing a new type of steel… the fundamentals of steel aren't changing," Dennis notes.
But our climate is. The problem isn't just heat, but extreme swings in temperature, says Fujiyama, that causes buckling. Plus, steel can only withstand that limited temperature range. "The way that climate's changing means we're getting more extremes – more extreme winters and more extreme summers," says Dennis. "That 60 degree sort of range that steel rails can cope with is starting to get pushed by the extremes in either direction." The more our climate changes, the worse your commute is going to get – and there's little we can do about it.
This article was originally published by WIRED UK
