I've seen a Waymo block the Muni tracks before. When a train finally showed up a cop appeared in less than a minute. They didn't jump in the car but they did knock on the window and speak to a support rep. The rep was able to instruct the car to move forward and turn onto a side street. It then blocked the side street for a bit before eventually moving on.

While I'm not against self-driving taxis I have some serious concerns over how these cars will impact emergency response in an earthquake or fire if the cars become more prevalent.