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.
The radios would need to have a very, very short range to avoid this. You’d need to know that everyone who can hear you can also see you (and potentially follow you if they’d like a word face to face), which is the accountability aspect that’s missing from online interactions.