Trains (and train-like options such as metros) are vastly more efficient than cars in number of people moved per unit of time per area used. That might not be a big deal in suburbia, but in dense inner cities it's one of the most important drivers of public transport.
What makes trains efficient has more to do with the cost of energy and drivers than anything else. Both of those go away if you have autonomous electrical vehicles.
A random crappy light rail line will do the equivalent of 5 lanes of traffic (each direction). A serious subway more like 20.
https://visual.ly/community/Infographics/transportation/solu...
Even if you run cars with no distance between the bumpers you'll still need room for changing lanes, crossing and the line.
We'll see how this plays out.
You also have to take into account all the other factors that make roads preferable, for example, that rail capacity number assumes perfect utilization. In practice railways often have lots of downtime due to overnight shutdowns, broken signals/trains and labor strikes. None of these affect the roads.
Private motor vehicles: 600 - 1600 per hour
Mixed traffic with frequent buses: 1000 - 2800 per hour
Two-way protected bikeway: 7500 per hour
Dedicated transit lane: 4000 - 8000 per hour
Sidewalk: 9000 per hour
On-street transitway, bus or rail: 10000 - 25000 per hour
https://nacto.org/publication/transit-street-design-guide/in...
And energy isn't free. If we had any intention of becoming net zero, electricity prices had better increase. And driving around 2t empty weight isn't the way to get there.
Incidentally, a trip that's less than 1 kWh (so, less than 6 km) is a trip that could easily be made on foot or by bike.
2. They will need stop some time. Where? Will this block the street?
3. They won’t all go to the same place so there will be delays at junction and side streets
4. No margin for error wouldn’t fly in practice, so the cars cannot be that close together
5. How will pedestrians cross a train of cars?
I just don’t see how this all adds up. Automation doesn’t remove the space constraints of cars in cities.
A train line has 10x the capacity of a single lane of road. Even if trains are only coming every few minutes, its impossible to compete with a train carrying 1k people with cars. Perhaps reasonably loaded busses would be comparable or better, but that's not the argument you're making.
Trains are financially efficient because of cost of energy and drivers (and, arguably, roads + cars move much of the expense to the public, where as everything related to the train is on the operator's balance sheet), but they are also very space efficient, compared to roads + cars.
