This is the basis of the SLAM algorithms (SLAM = simultaneous localization and mapping). As you say, if we all had these cars, we'd quickly know about changes.

This is the basis of the SLAM algorithms (SLAM = simultaneous localization and mapping). As you say, if we all had these cars, we'd quickly know about changes. Of course, the hard problem is finding the new lights, but if this was to become mainstream I think a lot of things would change. For example, if a town decides to install a red light, they don't just install one, they register it in a national database.