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.
I will add one more: a quick once-or-twice blink of the hazard lights indicates “thank you” if someone lets you merge in front of them, etc.
This seems analogous to the video game “Killing Floor”, albeit with much lower stakes. This game is an FPS, and playing it requires your attention. Voice chat exists, similar to CB radio in cars, but many people opt out, to avoid the distraction.
The game has a “quick chat” feature which cannot be disabled, which allows for messages like “follow me,” “get out of here”, “medic”, “thank you” and a few others.
Perhaps a quick chat system for cars would be an improvent over the ambiguous “hazard lights / high beams / honk” messages which can be misunderstood. I think we’ve all had the experience of wondering, “why were they flashing their lights at me, or were they just going over a bump in the road?”
Although the first concern would be to limit their potential for abuse / distraction.
Possible messages: