Whats the cost of the surrounding needed to have a moderately effective collective transport (improperly named public, since it's generally private, subsidized

Whats the cost of the surrounding needed to have a moderately effective collective transport (improperly named public, since it's generally private, subsidized by the public since being economically untenable)? Let's start from the need of density. In the past cities was a nightmare but a need, in the modern era they was the motor of any civilization since they was the place where ideas can be exchanged and so evolve, where most enterprises and customers and workers co-exist. But after the first logistic revolution in the '80s most productions have gone outside the city, in entirely artificial distopic district build around mega-factories, where worker's live, but not where customers live, without really exchange of ideas being "isolated big factories". With TLC/IT (bad) evolution we finally got enough bandwidth and work models to work remotely, exchange ideas remotely, the new agorà is on the internet (BBS, nntp news, then the web). So? So, well, cities once needed for many reasons do exists only for very few reasons, the most prominent is being kind of labor camps for poor who live to work, to earn enough to pay services they need to live. Unable to substantially improve their condition since costs suck most of their earning. In that sense the cost of public transport is the cost of keeping up a decadent gigantic structure: the city. A shared cost with some other cleptocratic business, but nothing else. This cost is HUGE. Some, let's say McKinsey dream flying cars https://www.easa.europa.eu/sites/default/files/dfu/uam-full-report.pdf https://www.easa.europa.eu/sites/default/files/dfu/uam-full-... and while I'm less optimistic in timetable and scalability terms that's the cheaper theoretical evolution we can hope for. Because IF we will been able to reach a point where we can move anything by air then we can give up roads who are one of the most expensive logistic infra we need anyway for low density area, far less expensive but since so many road not less expensive than the hyper expensive high speed and high capacity roads links between cities. IF we will reach such goal (and I'm pretty convinced not so fast, but we will) than the best density balance will be leaving and working spread in vast areas in small buildings, perhaps with just few district for things that we still can't do at smaller scale. As we chosen to go from mainframe to cluster, for mega-ship and mega-plane to smaller ones, so we will do for living. Collective transportation does not fit AT ALL despite the contrary interested propaganda.