Ok, fair enough - for urban centers. Although to your first point, lets go farther and say that 50% of core city streets could be closed to traffic and repurposed for walking/biking pedestrians.

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So... this got really long. It was just supposed be a quick back-of-the-napkin sanity check estimate of the economics of some rural autonomous vehicle service scenarious and it got a little out of hand. If anyone else also finds this interesting, drop me a line or comment!
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Lets also consider the merits of these two transportation scenarios when depoloyed to serve regional/rural populations too. I don't think any of these benefits are significant for the other much less dense half of the US population (but by 2033 or something this fraction will fall to like 1/3 I've heard).

I grew up in Northern Michigan, where 99% of all daily trips were between 5-40 miles and required a personal car because there was no availability of taxis (too expensive per ride) or buses (because population density was too low to marshal enough passengers per bus route). In cities, where density is high and distances are low, buses/trains that batch passengers into one vehicle that's part of an interchange network works pretty well. But in rural areas where the opposite is true, passengers can't be batched together as easily, so buses don't work and an interchange takes too long to transit because of the distances.

A personal car is a necessity for most people living in rural areas because there is no other practical way to get to a job, store, movie, friends house, hospital etc when these locations may be 10-40 miles away. The time spent traveling to these places may be about the same as the commute time for a city-dweller, but rural residents have to do the driving themselves. Aha, so the critical question is: what, if any, features of personal transportation via on-demand self-driving-cars-as-a-service in rural areas might make it competitive with or more desirable than owning a personal car?

If costs per year are roughly equal, then I would love a self-driving car that I could work in. Or self-driving land-yacht office RV for 4-8 people.

Say a personal car costs $3000-6000/year in gas, maintenence, payments, etc. If a person travels 200 days a year and takes 2 trips a day, that's 400 trips a year. This is hard to estimate. To be conservative lets say self-driving-cars-as-a-service would be competitive if it allowed a customer to take 400-800 trips a year for the price of owning a car. That works out to $3.75-$7.5 per trip for the ex-owner of a cheap car, and $7.5-$15 per trip for the ex-owner of a mid-range car. I guess if these are electric self-driving cars, the fuel cost might be $0.50-$2 per day. Hmmmm. If the vehicle cost ~$50,000 and the profit per ride was $4, then it would take ~12,500 rides to break even. If a vehicle can get 10 average fares per day, 350 days a year, thats 700 fares per year.

So actually, the economics are not toally insane. At $4 profit per ride, it would take ~2 years to break even on a $50,000 vehicle assuming 10 rides a day that that take 1 hour, have a rider only one of those two ways, and only have 1 rider at a time. These vehicles might be operating at 20 hours a day though. Not sure they would last 2 years. So... what startups are working on self-driving Land Yacht Office co-working-commuting vehicles?

Now I see a significant portion of the fleet should be something that could pick up at least a few passengers along a route, otherwise there would need to be basically as many vehicles in the fleet as there are riders to support solo rides during commuting hours. $200,000 land yacht, 5 riders, $5/ride: 8000 trips to break even, 10 rides a day = ~2 years. But for a region of 40,000 riders, that might require 5000-8000 land yachts that cost $200,000; so $1-1.6 billion in vehicle costs. Aw man. What's ubers valuation? 70bn? And goog is 820bn? hmm.

Ah so here's the problem. Because of the distances involved in rural trips, it might take 15-60 minutes after requesting a ride for an automated fleet vehicle to travel to the pickup location. That might be ok for occasional travel, especially if trip times are 3+ hours, but it wouldn't be convenient for daily travel. So rural passengers would probably prefer owning their own car, or sharing an automated land-yacht with a couple local other folks, because they need it to be physically nearby most of the time to minimize the time-to-pickup.

In conclusion, InitialLastName's comment leads me to imagine a future in which the dense core of urban areas is served by high-capacity public transit, a significant portion of the central surface streets are closed and used for other purposes, with small-vehicle parking and pick-up/drop-off hubs are sprinkled throughout and around the city that link transport throughtout the wider region and state via privately owned vehicles (for daily commuters) and automated on-demand vehicle fleets (rolling offices) for the ocassional traveler.

Personally, I find it hard to do productive work on public transit, largely because transfers interrupt continuous work and the passenger compartments prioritize density over work surfaces. I think I would be ok paying 2x the fare of public transit for a trip that took 1.5x as long if the vehicle was outfitted with normal office furniture (desks) ~6 passengers. A relatively low-density vehicle for its size, scheduled a couple of hours in advance, providing a hub-to-door trip with no transfers. Ha. Yeah. Self-driving-land-yacht-office-as-a-service company?*

* we could validate it right now... SF <-> Palo Alto, 6 round trips per day per vehicle, 6 passengers per trip, $19 fare, $200,000 vehicle cost, $19/hr for driver, and lets ignore fuel costs. So say revenue of $600/day, that leads the vehicle break-even within a year. hmmmmmmmmmmm.