Support for real-time traffic is crucial to many ITS (Intelligent Transport Systems) safety applications. At the same time it is desirable to support a number of non-safety applications. Based on a merge assistance scenario supported by roadside infrastructure, we propose dynamic data traffic priority classes based on parameters like position, speed and road traffic density. Moreover, we discuss both how to schedule data traffic in order to support the QoS demands of both safety-critical and non-safety critical traffic classes and how to analyze the real-time performance of the network.