Maybe it's just me but that picture makes the exact opposite point from what you're saying. It clearly points out that the difference between cars and other forms of transportation is linear. Public transportation doesn't scale this especially well, as anybody using public transport knows, but this article is a nice summary [1].

We all know what would happen to bus stops, stations, and generally to public places if people on buses actually had anywhere near the density "made possible" by public transport. It just won't work.

While for instance, adding roads in the sky (ie. very long bridges) scales exponentially, for obvious reasons. As does just flying (flying, incidentally, is a lot more efficient than people think). People don't want this, for obvious reasons, but there comes a point in cities where we have no choice. Frankly, cities like depicted in "the fifth element" and "star wars" are the future. Probably more rails, less floating, but the general idea is where we'll be going.

Doesn't even really matter if they have public or private transport. Given how fast public transport upgrades (even when absolutely required by the numbers of people they just refuse to upgrade for decades. Yes. Decades) and how comfortable it is, and add of course the fact that they just don't support the use cases cars enable (some of which, like an elderly or disabled person doing groceries, are absolute requirements) and you get to the point : private transport is far preferable to public transport.

[1] http://www.uwgb.edu/DutchS/PSEUDOSC/MassTransit.HTM