Crossrail (the project which is to be branded "Elizabeth Line" although all the other "lines" are lines within some larger modal network, so arguably this branding makes no sense) was a huge project. From funding to today it's ten years and the basic idea (East-West tunnels through central London) is from the mid-20th century.

It's taken so long that projected peak system congestion _with_ the extra line is predicted to be worse than it was without the line when it was funded, even though its capacity is about 10 passengers per second through the core. The lines it's "relieving" are hopelessly over-capacity, so it will fill immediately when it opens AND it's expected to increase total usage because hey, there's this line from outside London right into the core, why not live there and commute...

But certainly it's a comparable problem, in the sense that e.g. Crossrail had to "thread the needle" fitting the new tunnels between existing escalators and the Northern Line underground rail tunnel that both remained in use during construction.

> From funding to today it's ten years

This seems pretty reasonable to me, to be honest. And most of it is done ahead of schedule isn't it?

How quickly do you think it should take from zero to a 21 km tunnel underneath London? It seems insanely fast now I think about it.

Very fast. And not just that. A big part of the cost and complexity of Crossrail isn't the tunnelling but rather the (re)builds of the stations, the remodelling and reconstruction of the above-ground street areas to increase capacity there too, and many other subtleties that people don't tend to think about.

It's the biggest civil engineering project in Europe, or so they say. And a big part of that is because you don't just massively increase transport capacity into the core of a major metro area. That would just overload all the other infrastructure.

> A big part of the cost and complexity of Crossrail isn't the tunnelling but rather the (re)builds of the stations, the remodelling and reconstruction of the above-ground street areas to increase capacity there too, and many other subtleties that people don't tend to think about.

The BBC's documentaries on the Crossrail are great at showing all of the complexity of building the thing and dealing with historic buildings, super-hard brickwork, archaeological discoveries, concert halls and more.

https://www.youtube.com/watch?v=SD77jr6M6cs

Crossrail is a well-done project. But just to be clear: there were fully 68 years of feasibility and planning studies prior to getting the funding for construction. Since then, it's been laudably smooth sailing -- but if one considers the pre-construction planning work, there's substantial room for improvement.