Beijing Subway--which barely existed 20 years ago--is now the world's busiest; has pretty wild rolling stockpic.twitter.com/8YRyt1KQSZ
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You will notice that Tokyo's subway exists as a subset of a much more comprehensive suburban rail system, unlike Shanghai or Beijing
Compare: Tokyo subway network vs Tokyo railway network (includes subways)pic.twitter.com/93MpqG8nm8
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