But is it only BER? As mentioned int the article - what about Stuttgart 21 ( https://en.wikipedia.org/wiki/Stuttgart_21 ) etc.? It is possible that these sites exist as new financial "loopholes", transferring tax-money from the government to private contractors without much oversight.
The complexity of that project is extremely high. My cousin is a civil engineer in Stuttgart, and he showed me a cross-sectional diagram of the affected area and the number of considerations seemed intractably high to me. But more generally, these kinds of megaprojects go over budget in nearly every part of the world -- especially when tunneling is involved. Here in the United States, two examples are Boston's "Big D…
https://de.wikipedia.org/wiki/Neue_Eisenbahn-Alpentransversa... (German)