V2X communication - communication between vehicles (V2V) and between vehicles and infrastructure (V2I) - promises new methods for traffic management by supplying new data and by opening new ways to inform drivers about the current situation on the roads. Currently, V2X cooperative systems are under development, forced by both the industry and by the European Commission which supports the development as a part of its Intelligent Car Initiative. Within this publication, "iTETRIS", a new system for simulating V2X-based traffic management applications is described which aims on high-quality simulations of large areas. This is achieved by coupling two well-known open source simulators. The sustainability of the project is guaranteed by making the whole also available as an open source tool.