I don't see how setting up an entire new parallel road network all over the world is "less ambitious". Some of the best funded cities in this country aren't even able to lay a few miles of fiber for broadband internet.
Cities usually go as far as having dedicated lanes for buses on a few main thoroughfares. That is a far cry from having a self driving car not encounter any human driver during the drive from my home to my office or the grocery store, for example.
The goal is not to never encounter a car, but that the encounter is mediated with very robust and proven technology that is compatible with both human and current level AI, like a V2X enabled trafic light or a steel bollard. A car can still hit the pod if it disobeys the red light, but the driver would be culpable and the incident itself would be similar to a car hitting, say, a bike - not the fault of the bike.
As for the density of such infrastructure, you don't need it on every street, just within a short walking distance to be practical, a few hundred meters maybe. Once you can reach the hail point, it can take you non-stop to any other in the area served, so something like 30 Km/h top speed can go a long way.
