The "real time" control loop between the sensor on one car and the brakes on the same car is much tighter than that between the sensor on this car and the brake

The "real time" control loop between the sensor on one car and the brakes on the same car is much tighter than that between the sensor on this car and the brakes on another car and then feedback from the other car that braking has started. I don't actually know how long it takes between the computer deciding to brake and the car actually starting to slow down, but I expect you can't just throw out a message saying "I'm braking immediately" and start braking without any kind of confirmation that the message was received, and expect it to be OK. But maybe you can afford to wait for a confirmation? The speed of light is pretty fast, and you're not transmitting that many bytes. Especially if you consider that a human could easily take 200 milliseconds to react to something even if it's really paying attention. You could request a braking confirmation from the other side of the Atlantic and still come out ahead!