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 do a lot of water sports in the UK and we use VHF radios. Certain frequencies are used by marinas and the like, and nearby boats will be tuned into them. Then there is a frequency used for emergency calls - the coastguard listens on that and answers, and will move your call to another frequency for more details, leaving the mayday one open again.
We mainly use VHF for boat-to-boat comms, or boat-to-shore. The local range is decent - a few miles from our base, depending on atmospheric conditions, obstacles etc. I honestly have no idea if you could use VHF radios between cars though. It’s not private for a start - everyone can hear you - and once someone is yammering on the marina frequency no-one else can transmit. So it’s just brief messages with protocols.