Lots of European cities built these systems after WW2. Lots of Chinese cities have been doing it since the 2000s. Apparently it makes sense. When I see that a city like Seattle is not able to build mass transit between west and east side, and instead is maintaining gridlocked 10 lane "free"-ways and wider bridges I find that very comical. It is one of the main reasons I feel alienated every time I visit the area.