I will add one more: a quick once-or-twice blink of the hazard lights indicates “thank you” if someone let’s 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.

Although the first concern would be to limit their potential for abuse / distraction.

Possible messages:

1. My vehicle is stopped
2. My vehicle is moving slowly
3. Hazard ahead
4. Let me pass
5. Wait
6. Thank you
7. Turn on your headlights
8. Turn off your high beams
9. You have a light out
10. Something is wrong with your vehicle