It's very hard to really gauge the impact this has on human productivity, especially given that in public transit you don't need to control your vehicle and so can be doing something else (although from my anecdotal experience, the vast majority of public transiters are doing nothing productive or interesting on their commutes).

But then there is also that, when a global pandemic happens and localities lockdown public transit, people with cars can still go places (like a National Park).

Point being, the problem is absolutely not one-dimensional and so just comparing aggregate expense is not very useful at all.

I think the goal for transport should be to maximize human productivity and mobility, and given the above and other realities, that almost always means a strong hybrid approach, not one where you relegate cars to a lesser status.

I suspect that to make real progress we will need to move away from our current assumptions. I'm not from the US, where perhaps the expectations and practicalities of transportation can be quite different to somewhere like Europe. But even here, there is a tendency to conflate mass transportation (buses, trains, etc.) with public transportation (vehicles run as a service by someone else, rather than owned personally and reserved exclusively for the use of their owner). As the existence of alternatives like taxis and school minibuses demonstrates, these are really two separate axes. And that's before we get to all the complexities of how we pay for transportation, both individually and as a society collectively.

There are some big advantages to providing individual transportation tailored to each specific journey. Going door to door at an exact time of their choosing can obviously be more efficient, sometimes several times more efficient, for the individual traveller than having to connect to and travel via a network of predefined locations on a predetermined timetable. There are also some health and security implications for travelling individually, and of course it can be much more comfortable because you have plenty of space, a guaranteed seat, your preferred temperature and ventilation levels, etc.

There are also some big downsides to individual transportation using the options we typically have available today. In particular, the individual vehicles we use right now are often not well suited to any particular journey. People are more likely to own a single vehicle, which they use for anything from taking their whole family on a long distance journey to a one-person drive to work or for shopping. That can be very inefficient in terms of space usage, environmental impact and operating costs. But then owning multiple vehicles, suitably sized and featured for different types of journey, is also very inefficient if each of them then spends most of the time sitting idle in a garage somewhere. And there are safety implications for using a smaller personal vehicle on the same roads as bigger, more dangerous vehicles operated by fallible drivers, as anyone who cycles around a big city can testify.

On top of that, you have an emergent system where there are millions of individual journeys happening on the same infrastructure with at best some very local co-ordination via things like lights at junctions. If you look at the mathematics underlying transport networks, you can see how this can lead to all kinds of surprising and sometimes very unhelpful overall outcomes, even if everyone is acting logically as an individual part of the system.

But there is no rule that says things always have to be this way. Sometimes mass transit uses dedicated infrastructure, as with trains and planes, and sometimes it's shared with individual transport, as with most buses and trams. Future infrastructure could be designed to support, as one possible example, both small and efficient personal vehicles and larger vehicles with space for more passengers and/or cargo that could be summoned on request, with preferred routes and timing specified by each traveller, but with the actual co-ordination of the vehicles administered centrally and the vehicles themselves operating autonomously.

It's obviously a huge jump from where we are today to such a system, and there would be all kinds of difficult questions about how we could migrate from one to the other even if we somehow all agreed on where we were ultimately trying to reach. But one thing is for sure: we can't even start working towards a system like that as long as we stick to preconceived notions of public transportation as mass transit with fixed timetables on large vehicles like buses or trains, and private transport as the family car as we know it today.

Isn't there a bureaucratic problem hiding in that observation? Some money is saved by police and by individuals who would have crashed, but the departments responsible for upgrading the infrastructure will never get a return on their investment. In practice that'll mean higher taxes to support some new-fangled tech that doesn't immediately help the majority of people, and I'd be surprised if that gets support.

Our bus system where I live travels with many busses nearly empty. This is what happens when they are funded by a percentage of property taxes rather than individuals paying per ride. A perfect example of government waste.

The roads could have captors/sensors/tags added gradually to them. For example, some near field devices planted in the road and broadcasting information such as the name of the road, mile mark, line number/side or traffic lights broadcasting if they are at red or yellow or green or signs such as Stops broadcasting their presence.

This would help autonomous vehicles a lot (instead of having to scan the infrastructure and deduce the environment, the infrastructure will broadcast the environment, at least the static parts, directly), while at the same time not be that costly (compared to the initial cost of the road or even its maintenance costs).