I can imagine NYC with 1/10th the private cars and 4x the shared/rental/taxi cars, and traffic flowing much better than today owing to the additional bandwidth freed up by the 70-80% reduction in street-side parking space need.
As an NYC resident, I would much prefer to just have 1/10th the private cars, twice the number of trains (or whatever is necessary), and a massive reduction in the number of cars sitting around unused, with the resulting extra space being converted to green space, pedestrian-only areas, and bike lanes. Self-driving cars and the infrastructure they necessitate would make NYC more hostile to people, not less.
Train infrastructure is simply not economical by comparison to buses. You could have a bus system as good as, say, Buenos Aires, if you were willing to let it be run by the private sector. Cars are not entirely replaceable by trains and buses. But if you replace N privately-owned, mostly unused cars with N/10 privately-owned _shared_/rental/taxi cars whose utilization is much more than 10x that of the average privately-owned non-shared/rental/taxi car in the city, then you win big even if you also improve buses and even trains.
I would be happy with more buses or trams or any other kind of mass transit option. As long as the space taken up by private cars is drastically reduced and the resulting space repurposed for actual public use. Public space is currently completely wasted by being disproportionately allocated for cars, many of them completely unused and taking up space for free.
Buses and trains may not completely serve all the needs which cars can, but almost all of the remaining transit needs can be easily taken care of by bicycles, which should also be a much higher priority in the city. Either way, it really is a no-brainer that we must de-prioritise cars.
As a non-NYC resident, I would love to see the same thing in my town.
I don't want to piss away $40,000 + another $80,000 on maintenance and insurance and parking fees and bridge tolls on a self-driving car that will stand idle in my garage, or my employer's parking space for 23 hours of the day. I want better rail. I want more buses. I want to be able to ride a bike, without putting my life in the hands of lunatics who in any sane world, should not have been licensed to drive.
Surely, we could deliver all that for the money we are currently wasting on automobiles?
I doubt you could deliver better rail for that money. Rail is fantastically expensive, and if you get the routes wrong, that's a forever mistake. Buses are another story, but even NYC, which has the density to support a fantastic bus system... has a crap bus system.
Owning a car in a metro area is ~$8,000/year. There's 1.3 cars/household, so we're looking at ~$10,000/year/household.
My metro area's per-household budget is ~$17,000/year. ~$4,000/year on that is spent on transportation, including public transit, roadway, and highway maintenance and construction.
Tripling the transportation budget, at the expense of personal automobiles would absolutely deliver many of those things.
NYC has a crap bus system, because they have to share roadways with automobiles, which are the cause of NYC gridlock. If buses had the right of way, they would work much better. And it doesn't take being Nostradamus to figure out at least a couple of good, new train routes - in any metro area.
I'm sure you could find me some examples of train routes that were built, and then turned out to be under-utilized... But I feel that they would be the exceptions that prove the rule. Every major metro area is seeing population growth, so it's not like people will suddenly move away from the train lines. Not to mention that every line of rail tracks has the throughput of a super-highway[1], at much smaller footprint and cost (If you take into account the full cost of vehicle ownership.)
[1] In Vancouver, any one of the three SkyTrain lines has a throughput of ~14 lanes of highway, during peak hour...
I wouldn't exactly say that rail is fantastically expensive. Acquiring dedicated right-of-way for any form of transportation (rail, bus, car) through a developed area is fantastically expensive. But metal rails and overhead wires cost about the same as 12 feet of asphalt. And in terms of capacity, one track of rail moves +10k people per hour, while a lane of highway with personal cars moves about 2k to 3k [1]. Bus Rapid Transit is a nice middle ground because it has a little less capacity than trains but can be installed in existing right-of-way - like a road with 2 lanes in each direction or a lane of parking. So to me, better bus networks are about optimizing existing infrastructure. However cities still need to engage in new infrastructure projects as they grow, and it's often hard to beat the cost per capacity of rail in a new project: A line in each direction get's you the capacity of a multi-lane highway in a fraction of the real estate.
And in terms routing railways - it's really not that big of a deal. If you create a fast and economical route between two places, market forces tend to move people along that route eventually. Now you might have decades of an unprofitable line before you build up enough density to really take advantage of all that capacity, but it will happen... assuming it maintains support from politicians.
Rail is not a short-term solution, but it's a great investment in the long-term health of many cities.
NYC residents just might accept the trade-off.