@trapezius @[email protected] None, because in places where efficient mass transport can make a profit, either it's been done by the public sector already (e.g. Tokyo, Seoul, Singapore, Berlin...) or the government is so dysfunctional that if a private firm did start such a line the city would extract all profits through bullshit regulations.

EDIT: I wrote about it 2.5 year ago: https://pedestrianobservations.com/2020/06/14/the-problem-of-infrastructure-profits/