In London it is illegal for a person who has the plague, knowingly, to flag down a taxi and try to ride a bus. This seems quite obvious to me that if you have the plague, or any of the other notifiable diseases including rabies and leprosy, that taking public transport shouldn't really be an option for you. However apparently it needs to be in writing, as it is, in a part of the  Public Health (Control of Disease) Act 1984. Although this is unlikely, the plague could spread throughout a city as in urban areas with high rat infestations, the plague can pass between fleas and rats. If this somehow happens and you are unfortunate enough to contract one of these diseases, the taxi driver is actually allowed to let the you in, as long as they have their taxi immediately disinfected afterwards. However when it comes to the bus you have no chance as it is illegal for the driver to let you on. If only there laws for stopping a person with a horrific cold onto the bus.