I think the problem here is that it's very hard to enforce and requires everyone to open car doors in an unintuitive way. What would be better is an automated s

I think the problem here is that it's very hard to enforce and requires everyone to open car doors in an unintuitive way. What would be better is an automated system, say something that flashed the rear lights and made a sound before the door opened. Then you would have 100% compliance and people could still open doors in the way that they are accustomed to (which will probably happen anyway). This really is a case where a technological solution is superior to a behavioral solution, and this often happens in the realm of safety. E.g. instead of demanding that drivers give proper distance to cyclists, what we really need is a separate grade that enforces a proper distance. One is a poor substitute for the other, and when you are talking about safety, you want the technical solution over trusting that everyone will voluntarily always do the right thing to avoid an accident.