Comment by bluGill

there is nothing new about trains - we need to stop looking for innovation and just build them with small incremental improvements. The only useful innovation since 1920 is full automation (though I'm going to call high speed rail incremental since it is mostly a lot of small improvements on the way - this is debatable). Even full automation was a lot of incremental improvements.

That said, full automation is a major game changer because it enables short trains with high frequency which you would otherwise struggle to afford. Don't build light rail, build light metro which is a small cost more (build a metro with light rail) but now you can have full automation.