Zürich recently built a train tunnel that is 4.8 km long plus a 675 m trainstation 16m underground for ~USD 2 billion. https://en.m.wikipedia.org/wiki/Weinberg

Zürich recently built a train tunnel that is 4.8 km long plus a 675 m trainstation 16m underground for ~USD 2 billion. https://en.m.wikipedia.org/wiki/Weinberg_Tunnel https://en.m.wikipedia.org/wiki/Weinberg_Tunnel https://www.zvv.ch/zvv/de/ueber-uns/projekte/durchmesserlinie.html https://www.zvv.ch/zvv/de/ueber-uns/projekte/durchmesserlini...