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One third of the population of Switzerland lives within 5 kilometers of the main train line crossing the country
(reddthat.com)
Source (yes sorry it's LinkedIn, if you any another one, I'll update): https://www.linkedin.com/posts/prof-stefan-michel_notsweden-train-activity-7210174690827370496-8iJz?utm_source=share&utm_medium=member_ios
But train lines develops cities. I know that when a train line that connects big cities extends to smaller town they boom.