GoA 4 (no trained personnel onboard) is only practical for entirely grade separated (ie it's almost impossible for anything else to be there, no cars, no bicycles, no pedestrians) routes.
Even GoA 3 is fraught without this constraint, and for GoA 2 you're still paying for a driver because although the machine does most of the work the human has to handle the inevitable deviations from the model.
GoA 4 railways exist, if you're putting a metro in tunnels or elevating it obviously this is grade separated, and in principle you can do it for long distance rail if you're willing to eliminate at grade crossings (expensive). But they are nothing like a city bus route for example.
Even GoA 3 is fraught without this constraint, and for GoA 2 you're still paying for a driver because although the machine does most of the work the human has to handle the inevitable deviations from the model.
GoA 4 railways exist, if you're putting a metro in tunnels or elevating it obviously this is grade separated, and in principle you can do it for long distance rail if you're willing to eliminate at grade crossings (expensive). But they are nothing like a city bus route for example.