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Comment by untog | Hacker News Reader

It costs a lot because of political reasons. There’s no technical reason why NYC subway construction should cost 10x what it does in Paris, and yet, it does.

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NYC has more skyscrapers above to worry about below.

Paris has more historical buildings to worry about. Is there data on the relative added cost of either?

Paris isn't built directly on bedrock either.

But the trains run underneath the streets, not the skyscrapers.

Yes, but the foundations of the skyscrapers (which can go as much as 250ft underground) are where you'd want to build the subway. So you can't. You either have to go deeper ($$$$) or around (longer, again $$$). Plus, you have to make sure you don't dig out too much in the wrong place and cause a building to fail.

Uh, no they aren't. Look closely at maps of the NYC subway: with very few exceptions, the lines run directly underneath the streets themselves. Even many of the curves to traverse to following a different street occurs underneath the street right-of-way or the underneath parks. I count just five places where the subway runs underneath a tall building, and I believe in all but one of those cases, it's the subway that predates the building.

That's not the point. Digging a massive hole in the ground directly next to a skyscraper's foundation changes the physical properties of that foundation, and requires some very complicated engineering to get around it.

That and all the Manhattan Schist that needs to be excavated. New York certainly isn't built on mud.

O god. The Manhattan Schist takes ages to dig through and often involves blasting under the streets of NY because it's basically obsidian.

Tokyo, London, Singapore all also have lower costs and plenty of skyscrapers

Deteriorating infrastructure that drains all the resources is not a political reason, but quite practical. Though what caused that in the first place could be political in the past. I.e. bad planning and poor management. Today it's not political. Someone just has to deal with huge existing mess.

It's political today. These projects are given to friends of politicians at inflated prices and are used as sops to specific communities to stop them from kicking up a fuss or backing someone else. Here's the classic story of how costs can spiral without reason https://www.nytimes.com/2017/12/28/nyregion/new-york-subway-...

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