For smart traffic applications like dynamic route planning, communication between traffic participants is of high importance. Traditional communication architectures for smart traffic are centralized, which leads to major privacy concerns since every service provider gains a global view on the mobility behavior of all participating nodes. Recent publications on decentralized alternatives often claim to remedy privacy issues by getting rid of the centralized entity. In this paper, we test this assumption thoroughly, evaluating the privacy-aspects of overlay-based geocast systems in comparison to centralized approaches. To this means, we define an attacker model and describe two different attacks on privacy. Through simulation we show that without additional protection mechanisms, the difficulty for placing surveillance on individual nodes is low. Based on the results, we discuss possible improvements and alternative communication approaches.