Have you been in one of these vehicles? There is an emergency stop. It's just not a brake. Are you assuming that people can better predict when it's safe to stop emergently? I've never seen data that shows that. If you are in a panic situation the emergency stop pulls over and stops as soon as it can do so safely. You can't break a bus or a train or a taxi. As a passenger you can request any of those to stop when safe to do so. Cars are death traps. People are dying in cars all the time. Driverless vehicles are a safer option and saying otherwise is either ignorance or pushing a luddite agenda.