The scenarios in your first paragraph can be handled by treating the controls of the car as an input for the self-driving system. The accelerator asks the self

The scenarios in your first paragraph can be handled by treating the controls of the car as an input for the self-driving system. The accelerator asks the self-driving system to move forwards, whilst the steering wheel asks it to turn into the street to your right/left. Or, recognise that the existing controls no longer fit the purpose and come up with a better way of giving such input. For example, you might just point to where the car should go, or say "stop here".