> Where would you park the self-driving cars then?
Providing dense parking garages gets a lot easier if it doesn't need to be omfortable for people to get to the cars and you don't need to be able to open the doors when parked etc.
But the overall need for parking will also drop if more cars are shared.
> Considering in most cases > 80% of cars are on the road at the same time during rush hours, you can't save much with self-driving cars — not more than with a well-working transit system already.
But self-driving cars can be used to augment the transit system too. E.g. complement buses with mini-buses and smaller cars to handle overflow. Imagine an Uber-like service with an option to "call a bus" to any number of nearby "bus stops" at a lower price than if you call a car. If a full size bus is within 5 minutes, with space free, it'll make you wait for that, otherwise it'll dispatch a regular car at the same discounted price.
You could do away with normal bus schedules in favour of having the buses follow the busiest stretches at any time of day, and use cheaper/smaller vehicles to take other passengers.
E.g. near me the main bus route is used by two very distinct groups of people who either intend to go quite far, or who intend to go to the nearby train stations or high streets in either direction from me. During certain parts of the day the riders are often dominated by one or the other, and you'd get far more efficient use if you could shuttle people between the train stations/high streets and the longer distances separately. Knowing the start/end of each journey would allow you to "sort" the riders accordingly and dispatch vehicles much closer to optimal.
> And the "increade density, reduce parking requirements" — if you do that, you can just improve transit, and get the same advantage.
See above - automated vehicles will change transit too, but there are lots of situations where people still want to go door to door and are willing to pay accordingly. E.g. I take the bus from the local train station and home most of the time, but if I'm in a rush I might not be able to wait. Sometimes currently that's frustrating as getting a taxi her normally will take me 5 minutes. If I'm in a rush and there's a bus <10 minutes away, there's certainly a non-zero chance that the taxi will be late and the bus fast, and the bus will arrive first and I have to consider if I want to cancel the taxi or wait and be later than if I'd just taken the bus in the first place.
With a "combo service" with guaranteed pickup from specific locations in <5m by either bus/min-bus/car at the same price depending on what's closest, I think you'd see a lot more people here opting for something like that than people who currently use the bus, which could very well have the effect of making it viable to use far more buses.
A lot of the car users I see here (London suburb) mostly use public transport anyway, and have the car as "just in case" that will be increasingly hard to justify with solutions like the above.
Couple that with increasing pressure to reduce the number of allowed parking spaces in new developments further and it will keep getting less desirable to own cars many places.
> People want to own a car, have it always available, and don't want to share.
Do they? A lot of people feel they need a car, but I think far fewer want a car if they felt they had better options. Personally I don't even have a drivers license. Sometimes think about getting one, but it's an annoying time commitment for little benefit, when I can have a car here with a driver in 5 minutes so I can relax and read or play a game while I get to my destination. Ten years ago it was more annoying, but now it's gotten to a point where I don't think I'll get a drivers license in my lifetime (I'm 40), as the inconveniences keep dropping. The one remaining thing that makes me sometimes wish I had a car is for road trips on holidays to places outside of bus routes where it's expensive to hire a driver - self driving cars will take away that inconvenience too.
A lot of people do want to own a car still, but I suspect that car ownership will start trending downwards very quickly once self-driving cars drive the cost of car sharing services down further and make it easier to provide better guaranteed availability and shorter waits and more flexibility (e.g. get whatever type of car you happen to need)
A lot of people also have conflicting wants. E.g. they may actually want to own a car, but want that next holiday more, and so opt out of car ownership once a shared one ends up sufficiently cheaper.