Sweden does actually have a point about his railways.
Rails, being made of steel, expand when hot and contract when cold, which is why they have expansion gaps in them at regular intervals - this is what causes the characteristic rhythm of traditional fishplated track, though modern continuous-welded track has oblique joints to remove those discontinuities. The gaps are carefully adjusted to accommodate the normal range of temperatures expected in that region, and calibrated to the local temperature at the time of laying.
Sweden has very cold winters, by most countries' standards (as does Finland). Colder than Britain's winters, certainly, by a factor of 10-20°C. Conversely, summers in Sweden may be very sunny at times, but not usually all that hot because the sun shines obliquely through a lot of atmosphere before reaching the ground; the raw insolation power per square metre of ground is about half that in the tropics, simply due to the inherent geometry of latitude. (Stick that in your pipe and smoke it, flat-earthers!)
The practical upshot is that Swedish railways are designed to accommodate a relatively cool range of temperatures, from say -30°C to +30°C if we assume the southern half of the country. Temperatures below this range in a severe winter may result in excessive rail tension, putting strain on fishplates which may break them - but the rails will still stay roughly in-line in such cases, so it is not terribly dangerous if a train runs over the break before it is discovered. Wartime experiments in America showed that it was remarkably difficult to *deliberately* cause a train derailment by locally damaging an otherwise well-built track.
Temperatures *above* the design range, however, can result in track buckles. The rails expand to fill the gaps, then exert increasing pressure against each other, being held in-line by the sleepers and ballast. If this lateral restraint is overwhelmed, the result is a sharp, unintended chicane in the track, which can easily cause a train to derail. Speed restrictions in hot weather are intended to reduce the lateral forces exerted by trains on the track, reducing the risk of buckles forming in its wake - or even directly under it. If it gets hot enough, the line may be closed entirely for safety.
Note also that the rails can be considerably hotter than the surrounding air, since the sun shines more directly on their upright form than on the ground at high latitudes, and they are typically a dark rusty colour. It is possible to reduce this effect by painting the webs of the rails white, but this has to be renewed regularly to remain effective.
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Sweden does actually have a point about his railways.
Rails, being made of steel, expand when hot and contract when cold, which is why they have expansion gaps in them at regular intervals - this is what causes the characteristic rhythm of traditional fishplated track, though modern continuous-welded track has oblique joints to remove those discontinuities. The gaps are carefully adjusted to accommodate the normal range of temperatures expected in that region, and calibrated to the local temperature at the time of laying.
Sweden has very cold winters, by most countries' standards (as does Finland). Colder than Britain's winters, certainly, by a factor of 10-20°C. Conversely, summers in Sweden may be very sunny at times, but not usually all that hot because the sun shines obliquely through a lot of atmosphere before reaching the ground; the raw insolation power per square metre of ground is about half that in the tropics, simply due to the inherent geometry of latitude. (Stick that in your pipe and smoke it, flat-earthers!)
The practical upshot is that Swedish railways are designed to accommodate a relatively cool range of temperatures, from say -30°C to +30°C if we assume the southern half of the country. Temperatures below this range in a severe winter may result in excessive rail tension, putting strain on fishplates which may break them - but the rails will still stay roughly in-line in such cases, so it is not terribly dangerous if a train runs over the break before it is discovered. Wartime experiments in America showed that it was remarkably difficult to *deliberately* cause a train derailment by locally damaging an otherwise well-built track.
Temperatures *above* the design range, however, can result in track buckles. The rails expand to fill the gaps, then exert increasing pressure against each other, being held in-line by the sleepers and ballast. If this lateral restraint is overwhelmed, the result is a sharp, unintended chicane in the track, which can easily cause a train to derail. Speed restrictions in hot weather are intended to reduce the lateral forces exerted by trains on the track, reducing the risk of buckles forming in its wake - or even directly under it. If it gets hot enough, the line may be closed entirely for safety.
Note also that the rails can be considerably hotter than the surrounding air, since the sun shines more directly on their upright form than on the ground at high latitudes, and they are typically a dark rusty colour. It is possible to reduce this effect by painting the webs of the rails white, but this has to be renewed regularly to remain effective.