It's very, very difficult to run trains with headways of under 2 minutes (as in, under two minutes from one train closing doors to the next train closing doors)

It's very, very difficult to run trains with headways of under 2 minutes (as in, under two minutes from one train closing doors to the next train closing doors). The record holder is apparently Paris Line 1 at 85 seconds during peak hours, and some lines of the Moscow Metro do 90 seconds. https://en.wikipedia.org/wiki/Headway https://en.wikipedia.org/wiki/Headway