I guess my wider point was that
today, 55% of the world’s population lives in urban areas, a proportion that is expected to increase to 68% by 2050.[1]
Urban commuter trains will have little effect on that ~45% of people who won't live near them even if they are built.
On the flip side, though, I guess, that doesn't mean we shouldn't build more train lines.
1. https://www.un.org/development/desa/en/news/population/2018-...
