The train rail has evolved a long way over 250 years, but hundreds of different rail sections are still used throughout the world. To the untrained eye they might all look the same, much in the way that cars all look the same -having four wheels, a windscreen and headlights. But on closer inspection there are differences between the rail used, for example, on the London Underground and on mainline UK track. And heavy-freight track is subtly different yet again.
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