[madeofpalk]

So I think the insight here is that, as with everything, it can only scale so far.

Here's a question though: is it easier to build a new underground tunnel now compared to 100(?) years ago? While previously there was a lot less existing infrastructure to have to worry about disturbing, these days we have a lot more advanced technology to make the process easier.

[namelost]

Chinese cities have grown tremendously large metro systems in a very short amount of time. China has 5 of the 10 longest metro systems, and 4 of them were started operating in the 90s or later. The Nanjing metro is the 6th longest in the world and was started running in 2005.

https://en.wikipedia.org/wiki/List_of_metro_systems#List

So the answer is a resounding yes, it is much easier to build metro systems than it was in the past. As long as you do so in China.