[karmicthreat]

So what I envision is a many layered network of signals between cars. You have a pretty wide diversity in the importance and latency requirements of various communications between the vehicles regardless of the medium used.

Something like "Stopping" or "Everyone Stop, accident" need to hit the wire as quickly as possible. Maybe order the message to the Emergency Stop hits the wire first and any further message information after. That way the message can bypass most of the communications stack in the receiving cars.

Less important information like "Deer on shoulder of road" can use much slower and more latent communications.

Distance is also going to play a part in how the cars communicate. If the car can see tons of low latency high priority messages then it will be more problematic to develop. If the low latency physical layer can only see maybe 100 ft around its self because it is low strength radio or IR based, then all the better. Loud wide area communications can go through a far more latent filtering system.

All of this also doesn't take into account that these systems should degrade gracefully. If the low latency portion fails, the high latency system should still see something and react.