Do the Rails not buckle in Spain?
July 19, 2016 12:58 PM   Subscribe

One one of the hottest days of the year here in the UK, train delays and outright cancellations are being explained as due to Hot Rails and the threat of rail buckling. Can someone explain this to me? More specifically why I have not heard of this in Southern countries such as Spain or Italy where temperatures like this (33C) are the norm during summer and where winters can be even colder.
posted by vacapinta to Science & Nature (13 answers total) 8 users marked this as a favorite
Can't answer the technical side of this, but can confirm that they were actually warning about this very thing on French radio this morning (trains have to run slower cuz rails expand, which is likely to lead to delays, is what they said).
posted by ClarissaWAM at 1:01 PM on July 19, 2016

From wikipedia:

Obviously, there is a temperature at which a given length of the rail fixed to the track would be equal to a given length of the unfixed rail. This is known as the "rail neutral temperature". Note that rail neutral temperature does not actually measure the temperature of the rail. It is simply a reference to the temperature of the uninstalled rail before it is affixed to the sleepers. Immediately after any rail is installed into sleepers and is clipped down it becomes susceptible to changes in temperature and reacts by attempting to expand and/or contract along its length. Rail Neutral Temperature does not exist in installed rail.

When working with rail (laying new track, repairing track, or changing the sleepers/ties), this rail is mechanically or thermally altered to achieve a measured length equivalent to a stress free temperature of 27 °C before it is clipped down. This action ensures that at a known temperature of 27 °C it is expected that there would be no thermal forces, either compressive or contractive, in the rail.

The process of stressing rail installs the proper stress free temperature so that there will be a greatly reduced risk of fracturing or buckling at the temperature extremes. Since environmental extremes will vary, there is no universally applied stress free temperature. In the UK all Continuous Welded Rail is stressed to 27 °C (81 °F), the mean summer rail temperature. US standards range from 35 to 43 °C (90 to 110 °F), depending in large part on expected temperature range over the course of a year in a given region.

posted by ghharr at 1:02 PM on July 19, 2016 [15 favorites]

The way to keep the tracks straight is to put down lots of ballast (rocks), tamp it well, and have significant amounts of ballast outside of the sleepers (ties). I suspect that hot weather locations take their ballast more seriously that cooler locations.

Another way to restrain the tracks is to ensure that metal clips are in place on the rails, on each side of the ties. This isolates the pressure of the expansion of the track, so that it does not transmit down the line. Perhaps the hot areas keep track of these clips, as well.
posted by Midnight Skulker at 1:06 PM on July 19, 2016

My guess is because those temperatures are not unusual in Spain and Italy, but until recently they were unusual in the UK. Therefore British infrastructure is built around usual temperatures, and Spanish/Italian infrastructure is built around their expected temperatures. You see the same sort of thing going on with choice of road surfaces in different countries. British road surfaces are pretty good at dealing with rain, because it rains all the time. When I moved to SoCal I saw that LA roads perform pitifully in wet weather, water is not well drained off to the side, potholes appear at a much higher frequency, and so on.
posted by Joh at 1:29 PM on July 19, 2016 [11 favorites]

To expand on ghharr's comment:

If a section of rail at 27C is a kilometre long it will be 7.5 Centimetres longer at 33C. Steel is really strong in tension but weak in compression (this is why we reinforce concrete) so that 7.5cm of compression force may cause buckling. It can be larger than 7.5 cm too because the rail may heat faster than the ambient temperature if sun is shining on it.
posted by Mitheral at 1:45 PM on July 19, 2016

We get this with commuter trains in the Boston area too, though generally not until temps get up into the 90s Fahrenheit (35C+). Some of the lines are more susceptible to "hot rail" than others, apparently because of variation in the way they were laid. We have also had problems related to cold rails in extreme winter temperatures.

I think they just lay the tracks with an expectation that they will work in *most* weather, because building them to work in all possible weather would be somewhere between "ruinously expensive" and "actually impossible." In historically hotter regions, they lay the rails to work in hotter temps, but if it's (relatively) very hot, you can get this issue just about anywhere.
posted by mskyle at 1:50 PM on July 19, 2016 [1 favorite]

Along the lines of what Joh says, the U.K. has actually had repeated problems during this century with its auto road surfaces melting. During the heat waves of last year there was talk about how the design of most buildings make them very bad at dissipating heat. So yeah, centuries' worth of accumulated infrastructure there is designed for more mild temperatures, compared even with other places around the world at the same latitude.
posted by XMLicious at 1:52 PM on July 19, 2016 [3 favorites]

It's a problem in Australia when our temps go way above expectations (more 45 degrees than 33 though). Also when it's a heat wave so there is no chance of cooldown.
posted by geek anachronism at 4:19 PM on July 19, 2016 [1 favorite]

I suspect that there's quite a few additional factors involved (educated guesses, rather than anything else): it was GWR with the biggest problems today, all due to speed restrictions between Paddington and Reading starting about 2:30. In terms of infrastructure, they're running a lot of high speed diesel locomotives on not a lot of track. So there's a combination of trains with high axle loads (due to only 8 powered axles for a 10 car train), high line speeds and accelerations, quite a lot of switching infrastructure (for depots and the suburban stations on the Greenford & stopping Reading lines), and not much space to put it all in.

So the acceleration and therefore, thespeed has to go down, and there isn't the spare capacity between London and Reading to fit everything in. And there isn't a great deal of contingency at the western ends of the routes, either, although my train home today didn't go through to Weston super Mare, turning at Bristol instead*.

So basically, it's the absurd amount of commuter traffic on the intercity lines into London. And the fact that temperature spiking to relatively unusual peaks very fast from fairly mediocre weather is going to be more of a shock than a steady increase in temperature to one that the infrastructure's stretched to before. Note that speed limits were precautionary, too. Perhaps Network Rail Great Western are a little more cautious than other lines might be. They've had some unpleasant crashes in the past 20 years, and I do think they feel it.

*Also, it went into Box tunnel at 95mph today, when it's normally 100.
posted by ambrosen at 4:54 PM on July 19, 2016 [1 favorite]

Infrastructure is generally built around 'normal' conditions plus a little wiggle room.
Normal given the conditions around the time it was built, which may be decades ago.
Local conditions may be outside of that normal range at present - for instance perhaps July's been hotter for longer than Julys had been in the 70s/80s when stretches of track had last been laid.
Maybe we're even entering a period where 'new normal's are going to have to be set?
(see also 100-year Floodplains)
posted by bartleby at 7:37 PM on July 19, 2016

The bit of technology that's supposed to deal with rail expansion is called an expansion joint or (as I've just found out) a breather switch.
A well-planned and modern, or frequently updated, rail system would typically be built around an expected range of temperature changes. If a given climate displays greater fluctuations in temperature, more relief spots are likely being built into the system than in countries with more constant temperatures.
Then again, countries with complex, difficult-to-maintain and basically old-fashioned rail systems perhaps haven't fully been able to put this way of thinking into practice; I would expect the UK to belong to the countries where the officially expected range of temperatures is rather narrow (no creaking frost, no blistering summers on average), while much of the system is also maybe not the most modern, and perhaps more prone to developing problems during a period of extreme heat than a lot of others. But that's a guess.
posted by Namlit at 10:56 PM on July 19, 2016

Expansion joints shouldn't be an issue in Britain (or Northern Ireland, but for obvious reasons that's a different system), where continuous welded rail's been the standard since 1959, and track renewal schedules are a lot faster than that. I suspect that this is the case for every developed world passenger rail network of any density, but I don't know that for a fact.
posted by ambrosen at 11:45 PM on July 19, 2016

Continuous welded rail explained here - along with the reason good ballasting and good connection to the sleepers are important and help the rail withstand larger extremes in temperature, and why "sun kink" or buckling due to warm weather is typically seen as a more serious problem than contraction and breakage due to cold weather.
posted by flug at 8:13 AM on July 20, 2016 [1 favorite]

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