Earlier quoted context omitted.
Cars in tunnels is a great idea, just like the subway: burry it so as to not impact life on the surface. Unfortunately, it is very expensive to operate that way. The easiest tunnels to build are the ones Paris did for their subway a century ago: dig up the soft limestone under the street, lay tracks, close it up. But you still need to deal with ventilation (especially for non-electric cars), fire suppressant, evacuat…
To avoid accidents and other dangers, I'd see a mechanism where you park your car in a pod, and the pod is on rails, and it is getting routed automatically to your destination, that way even "dumb cars" could use it. There's already a system in France where you can park your car on a train, but loading/unloading isn't optimized at all, it's like loading/unloading a ferry : some batch processing. A steaming process wo…
Really, the car would (should!) still be driving itself—it's the thing that gets certified on how to handle safety issues, after all; the car would just be given a dead-reckoning location target by the zone controller, which the car would get to as best it knows how, with the zone controller scanning to "see" when it had successfully boarded, just like with a human-driven car.
If there were few-enough human-driven cars, you could have a team of valet staff accompanying the train, acting as glue for the few human-driven cars in the pack.