"[A] bit fraught" is an understatement. Any excavation under the right of way in New York immediately runs into undocumented tunnels, steam conduits, sewers, and water pipelines from the past 400 years of development.

They're trying to map these things out but it will probably take more than a decade. Until that happens you can't even begin to budget for a new city-wide underground infrastructure project. Any project has to be point to point and focused.

Let alone the issue of the rats.

https://www.bloomberg.com/news/features/2017-08-10/nobody-kn...