https://pedestrianobservations.com/ and the less feisty https://transitcosts.com/ are the canonical sources on comparative infrastructure costs.
The collapse of the Ponte Morandi / Polcevera Viaduct was just a few years ago and is still fresh in the minds.[1][2]
[1]
https://en.wikipedia.org/wiki/Ponte_Morandi#Collapse
[2]
Police release new footage of doomed Morandi Bridge collapse in Genoa https://www.youtube.com/watch?v=V479srTBlAk
Genoa motorway bridge collapse caught on camera https://www.youtube.com/watch?v=_Pl0rsVdXxM
Fast, cheap, good. Pick none. The American construction mantra.
So far it's worked because of the reserve currency and technological progress. But the time of the American monopolar world is coming to an end. In twenty years, the bill will come due and instead of acting to liberate themselves, Americans will fall over themselves to justify their status quo - unable to reconcile the existential shame they feel at the thought that they inherited power the likes of which the world had never seen before and transformed it to impotence.
"The billionaires", "we do it to be safer", "the X are ruining it". All the while they drift into irrelevance, raging hopelessly at shadows while their own choices drive them to destruction
As I recall, the TBM used in NYC was “mannned” by 5x more workers than an identical machine in Paris. We’re talking like 50 people. France isn’t known for labor efficiency, but between the various labor agreements, minority/women owned employee and subcontractor requirements, etc that many extra hands were being paid. Whether they did anything is another story.
- station sizes (causing spend on stations to increase by a factor of 2)
- nonstandard systems (elevators, escalators, etc) (causing an increase over nominal best practices of approximately 1.35)
- inefficient procurement (how contracting works) (increase by a factor of 1.85, although this is a squishy)
- soft costs (design, planning, construction management, contingencies) (factor of 1.2, again fairly squishy)
- labor costs (factor of 1.5 over a well run transit system baseline)
so it's both the case that the labor costs are outrageous and that they're insufficient to explain the outrageous project costs.
Which is what I said, the difference in labor costs "helps", not that it's the sole explanation.