I've heard on and off for many years (15 years?) about ad-hoc wireless networks for cars. Whether it's car to car, or car to some devices on the ground (lane marking, stop lights) so it knows where it is at in relationship to the road and other cars - and it would know if the car ahead is going to break or slow down.

Now the cars are relying on cameras, lidar to figure things out. What has happened to putting sensors on the road to broadcast what/where the roads is. Is that out of the question now because of cost?