The use of floating car data is an interesting method to monitor traffic. Vehicles act as local traffic sensors and data from individual vehicles is aggregated into higher-level information. We propose a number of reusable organization abstractions and a software architecture to support a multi-agent approach applied to floating car data. The abstractions are based on the idea of hierarchical organizations which are used as units of data aggregation. In this approach, an agent is deployed on each vehicle. At the lowest level, nearby, vehicle agents collaborate to aggregate individual traffic data and distribute it to local clients such as traffic light controllers. At higher-levels, organizations are built up from lower-level organizations and represent specific aggregation interests such as the total congestion level in a specific area. A prototype was built, supporting a two-level organization structure, and is used in a simulated traffic environment as initial validation.