https://interactive.wttw.com/chicago-by-l/sidetracks/history-l
https://en.wikipedia.org/wiki/Chicago_L
https://interactive.wttw.com/chicago-by-l/sidetracks/how-cta-map-got-its-colors
https://www.transitchicago.com/rpm/
https://www.chicagomag.com/city-life/may-2019/once-and-for-all-is-it-the-chicago-el-el-l-or-l
Of course Paris & several other cities have elevated metro train lines, as well.
https://www.toureiffel.paris/en/news/visit/bir-hakeim-station-closed
