The fallback has to work reliably, certainly for the foreseeable future, when most cars won’t talk or listen to other cars, but probably also if all cars share

The fallback has to work reliably, certainly for the foreseeable future, when most cars won’t talk or listen to other cars, but probably also if all cars share the information, to handle the case where some car stops broadcasting due to a bug or hardware breakage, and if your fallback works reliably, you don’t need anything else. Because of that, there, for now, is little benefit w.r.t. safety in this (there may be benefits in efficiency, for example if enough tell the traffic system what they’re up to, so that the traffic system can optimize traffic lights) Also, I hope (but I know I’m wrong in that) nobody is going to say cyclists and pedestrians should do this, too. You shouldn’t require people to gear up with electronics before they can go on the street (even if mobile phones were enough to do that), so the fallback will have to be there forever. There also is work being done on this. For example, the EU has projects in this space (https://www.connectedautomateddriving.eu/ https://www.connectedautomateddriving.eu/)