Several years ago I backpacked from Berlin to Beijing, covering much of the distance in a third-class car on the Trans-Siberian Railway through Russia and Mongolia. One night I was shaken awake at 3 am on the Mongolian-Chinese border by what felt like a derailment. I jumped out of bed and stared bleary-eyed out the window as railway workers detached each carriage from its wheel assembly and swapped it for one that fit the Chinese railway gauge…