[toss1]

I would not specify that the communication can be considered fully Line Of Sight.

There are many intersections where the car would need to communicate with the crossing car and the intersecting road is behind a hill, trees, or building.

Yes, attacks are an enormous concern, but comms and hardware failure are also very significant & non-trivial to solve.

[eximius]

LOS was a poor choice of words. But on roads or highways within 500m is even smaller than LOS