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 keep a CB radio in my car, and have a few friends with them
It is actually really handy when you’re road tripping together in different cars to be able to just grab the mic and say something to the other vehicle when you need to stop for a bathroom break or you’re having an issue with your car or want to give them a heads-up about whatever.
If you’re fairly close together a set of cheap FRS walkie-talkies from Walmart does the job just as well. Probably worth stepping up to CB if you expect to lose sight of the other vehicle though, range is usually a bit better.
It’s especially handy if, like me, you go camping and such in rural areas with unreliable cell coverage.
You do occasionally also get helpful heads-ups from truckers if you’re listening to channel 19 about road conditions, police activity, traffic, etc. but mostly it’s just idiots babbling about conspiracy theories and immature bullshit.