I was watching this video of a live chicken trapped on a moving truck and thought it was strange that it’s not possible to say anything to them even when circumstances might warrant it. All we got is honking and waving. There could be a touchscreen interface with a map of nearby vehicles. It could be voice controllable or the passenger could do it for safety.
Extept in very rural areas there are far too many people around for it to be useful. Unless somehow we can enforce strict rules on what you are allowed to say.