This paper describes iRide (intelligent ride), an IP Multimedia Subsystem (IMS), Multimedia Broadcast Multicast Service (MBMS), and wireless sensor network (WSN) joint application. The core contributions of iRide are: IMS and WSN architectural integration on joint data processing and signaling levels, application logic for increased road safety, and network dimensioning for scalability and performance analysis. The iRide architecture is built and prototyped using IMS standard SIP (Session Initiation Protocol) and DIAMETER signaling together with 3GPP MBMS for more efficient service handling. OPNET simulations are used to conduct network dimensioning and performance analysis. Resource management in systems such as the one presented experiences several challenges in the form of bottlenecks and multicast dynamic group sizing is used as a key technique to make resources on the downlink data planemore efficiently managed. The efficiency of the proposed model for the downlink takes on a Skellam distribution shape which is used for performance modeling.