I mean, if the police try to stop the car for some reason and realize the driver ("responsible passenger"?) is not responding.
The solution will probably be some kind of override, but then you need to deal with unauthorized use of the override...
I wouldn't give the car a wireless override, because that's a massive fucking security hole and exactly how you get hackers remote controlling your car. The AI can just emulate human behaviour and pull over when there's flashing blue lights behind it.
Pretty sure current self driving cars can already be overridden in various ways
*. Maybe difficult for a single person to have all the tools nessesary, but a well funded police department should have the tools to remotely disable all the car's navigation systems if self driving cars got prevalent enough.
Additional coding for emergency lights probably isn't even necessary. I think they are already programmed to pull off to the side of the road when an active emergency services vehicle is detected. (It's illegal to not pull out of the way in most places after all.)
If I understand correctly self driving cars will also slow to a stop if boxed in in front and all legal driving lanes. It won't attempt to actively evade a slow controlled stop that the police already know how to perform, just with a self driving car it won't be trying to evade like an actual driver does. Ideally there will be less reasons for the police to try to stop someone in a car anyway.