Earlier quoted context omitted.
> "it's mostly a problem caused by the sheer population density" That might seem like the obvious reason, but it's not the case at all. Read up on the NYC subway and its recent problems and their causes. Politicians use the growth in ridership as a scapegoat. There's more to the story than that. There's no physical/mathematical reason why a metro system of a bigger scale is precluded from running well. Here's an arti…
Sorry, I meant that the experience for riders becomes miserable because of the population density (the third paragraph). If delays just meant waiting on an uncrowded platform for an uncrowded train, it wouldn't be nearly as much of a sore point. I certainly agree with you that population density isn't the root cause of the recent subway issues - as evidenced by the fact that Tokyo's train system is working just fine.
This is a reflection of under investment and lack of maintenance and upkeep which was exacerbated by Hurrixane Sandy damaging the subway system significantly. It brought the chickens home to roost.