Comment by kube-system

Only in lower density areas.

In high density regions, vehicles on surface roads can’t meet the passenger demand required. Even if you banned human drivers, the other human users introduce too much variability and delay (passengers loading and unloading, errant objects, cyclists and pedestrians, etc). Roll a dumpster in the street, and have a couple of jaywalkers, and the entire system crawls to a stop.

Controlled access is required to get even medium-high throughput. But these systems already exist, they are called personal rapid transit systems.