Vehicular ad hoe networks (VANETs) and vehicular communications are considered a milestone in improving the safety, efficiency and convenience in transportation. Vehicular ad hoe networks and many vehicular applications rely on periodic broadcast of the vehicles' location. For example, the location of vehicles can he used for detecting and avoiding collisions or geographical routing of data to disseminate warning messages. At the same time, this information can be used to track the users' whereabouts. Protecting the location privacy of the users of VANETs is important, because lack of privacy may hinder the broad acceptance of this technology. Frequently changing pseudonyms are commonly accepted as a solution to protect the privacy in VANETs. In this paper, we discuss their effectiveness and different methods to change pseudonyms. We introduce the context mix model that can be used to describe pseudonym change algorithms. Further, we asses in which situations, i.e. mix contexts, a pseudonym change is most effective and improves the privacy in vehicular environments.
