> It's more needed than ever with the rise of incredibly cheap, extremely convenient, on-demand private transportation. The availability of which increases productivity and drives overall GDP growth and prosperity

Yes, lowering the costs (in time, money, energy and space) of transit increases the efficiency of our economy. It also increases the demand for such.

> Why would the road infrastructure ever become unneeded?

You were the one who said that eliminating non-self-driving cars would triple the space efficiency (and probably increase the other efficiencies as well). Are you claiming that this would lead to a commensurate tripling of demand? Otherwise you are looking at having more road capacity than is needed.

The issue that I see is that the increase of demand spurred by self-driving cars and robot taxis will happen well BEFORE we reach the point where those self-driving cars provide increases in traffic capacity (space) efficiency.

This timing mis-match will further exacerbate traffic and parking problems in major cities (reduced time, energy and space efficiency). These costs fall directly on those who will increasingly be forced to live further away from work which will disproportionately impact the poor.

Of course, if you increase usage fees without providing effective mass transit systems, park-n-rides and last mile solutions then this also serves as a regressive tax on the poor. This is the problem with simply increasing gas taxes rather than finding ways to directly tax congestion.

> Usage fees for roads that are being used more efficiently than ever, to try to drive people to less efficient (for them) modes of transportation, is a recipe for suppressing growth. It's a regressive tax which disproportionately impacts the poor.

Without usage fees, self-driving cars will lead to roads being used less efficiently due to decreased usage of public transit and increased traffic. If you grant that mass transit is socially more efficient, then increased usage of that will lead to spurred growth.

It is the optimization of individual efficiency, with its associated externalized social costs, that will slow economic growth overall. Single occupant vehicles may be the most efficient choice for the individual, but if everyone drives, then the use of single occupant vehicles is less efficient than it would be if fewer people drove. This is the paradox of the "tragedy of the commons", it doesn't just hurt society but has a direct negative impact on your individual well being.

> Scooters are great. Scooters are "0.1" relative to cars "5,500,000" in the 2017 million-passenger miles table. Maybe that grows 1000x to be a "100".

I think you misunderstand. First I meant a "kick" scooter (or electric kick style scooter) as opposed to a "small motorcycle" scooter as I suspect you interpreted. Secondly, I am talking about their use as a "last-mile" option which you would never expect to account for a large number of passenger-miles as they are supposed to be used for very short trips and "last-mile" portions on longer trips.

Edit: As a side note, I doubt we will see the nationwide banning of person-driven vehicles in our lifetimes. Americans love their cars and I doubt you will see them taken away easily. I suspect we may see the banning of person-driven cars in city centers much sooner.