This paper investigates the scalable dissemination of data between vehicles. The application context of this wok is traffic information systems where cars are not only consumers but also producers of information. The key challenge in those systems is to ensure scalability in an environmnt where data is provided and requested by all participating vehicles in a large area. We discuss two fundamentally different approaches to this problem: using direct communiction between cars and compressing the data via aggregation versus relying on infrastructure. The latter approach can further be divided into client-server and peer-to-peer systems. We outine all three approaches and highlight their advantages and disadvantages.