David Friedman and others have come up with decentral ways to deal with complex externalities like disease transmission risk. You can read "Machinery of Freedom

David Friedman and others have come up with decentral ways to deal with complex externalities like disease transmission risk. You can read "Machinery of Freedom" for a taste of how this works. It would probably involve health insurance standards for the negotiation of transit rights, just like we have car insurance standards for the negotiation of vehicle transit rights.