In the UK, this seems to take an extraordinarily long time.
https://www.theguardian.com/business/2026/jan/13/northern-powerhouse-rail-project-pledge-funds
A partial replacement for a notoriously inefficient and expensive project is expected to start building in the 2030s and be ready by 2045. Plenty of people currently working and needing those lines will be retired by then.
I find it difficult to believe that some other countries, especially in Western Europe can't do this more quickly AND while proceeding in a fairly environmentally sound way. (rightly or wrongly some of the controversy about why HS2 was so expensive was connected with conservation. I would say nothing was wrong with the principle, it was just dealt with in an overly expensive way)