Yes, in much of the world there are mandatory passenger-facing emergency break levers in every carriage of passenger trains. The US is the outlier here.
And yes, passengers should absolutely be able to bring their vehicle to an immediate stop. It's an "emergency break"! Of course you need an emergency break in an autonomous car! What exact alternative are you proposing for when you're in an AI-operated car hurtling under the chassis of a white truck that it failed to detect in snow conditions?
It seems like an incredibly obvious and basic legislative requirement for self-driving cars to have some kind of immediate manual break for emergencies. I'm kind of shocked that that apparently isn't the case now?