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.
This is actually being worked on. Researchers are looking at adding a 4th light to stop lights. When enough “smart” cars get into the area they will talk to each other and the stop light to help control the flow of traffic. The 4th light is to tell you that is happening. When the cars leave the area, the turns off, and the light goes back to normal control mechanisms.