In this project,we use vehicular sensor networks(VSN) which consist of sensor nodes deployed on the vehicles to facilitate vehicular application.We apply such VSNs to prevent rear end collisions that are common accidents due to sharp stops.The proposed framework consists of Integrated VANET vehicle to vehicle communications,used to form a warning groups,where warning group is a set of vehicles that drive along the same lane.And it performs the gateway selection,advertisement,discovery and service migration between the gateways.Thus the adaptive mobile gateway management mechanism is proposed. Here we use IEEE 802.11 based VANETs and wide coverage of 3G networks.Vehicles are dynamically clustered and equipped with IEEE 802.11 and UTRAN interfaces are selected as vehicular gateways to link VANET to UMTS.