It is foreseeable that in the few upcoming years, real time traffic information, including road incidents notifications, will be collected and disseminated by mobile vehicles, thanks to their plethora of embedded sensors. Each vehicle can thus actively participate in sharing the collected information with the other peers forming an infrastructure-less self-organising network of vehicles. However, the fast development of applications in ITS field may result in an excessive load on such a network; therefore an efficient use of the available bandwidth is highly required. Not only should the size of the data inserted in the network be properly controlled, but also the extent of each message should be accurately defined. In this paper, we propose a distributed dissemination protocol for safety messages in urban areas, dubbed "Road-Casting Protocol (RCP)", which is based on a novel cooperative forwarding mechanism. Moreover, an accurate definition of the Region of Interest (RoI) (i.e. the geographical scope) of each broadcasted safety message is also devised to ensure better control of the network load. We have evaluated the efficiency of the RCP along with the proposed RoI definition using realistic simulations, based on an accurate propagation loss model for urban vehicular ad hoc network communications, and the obtained results show a substantial improvement, compared to state of the art schemes, in terms of enhanced packet delivery ratio up to higher than 95%, lower end-to-end delay and reduced network load.