One of the big problems autonomous cars are having is recognizing when a policeman on foot is signalling for a stop.
Which is kind of a problem, especially in the USA.
Where, the sanctions for running a police roadblock are not just economic...
I’d look to V2X emergency protocols to assist here. That said, it’s not the stopping part, it’s the hand waving that signals to continue along.
These fringe use-cases are the barrier to L5 systems but I believe we’ll see L4 ones in the near future.