## 1 Introduction  
The World Health Organization (WHO) report states that due to the presence of road traffic injuries [1], more than 1.3 million people die every year. Delays in perceiving and providing care for those victims increases the severity of injuries; delay of minutes may decide between life and death. Thus VANETs, an imminent part of Intelligent Transportation Systems (ITS), help in disseminating accident notifications immediately after the detection of such event through vehicle-to-vehicle and vehicle-to-road side units (RSUs) communications [2]. Even though RSUs are available in urban regions, we cannot expect the reachability of the RSU for the entire road length especially in highways connecting different states. Similarly, cellular systems are also not available in remote areas. Also,installing the infrastructure needed for supporting cellular technology and RSUs in such remote regions are costlier. Furthermore, there is no support for RSUs or cellular systems, Vehicle-to-Vehicle (V2V) communication through vehicular ad-hoc networks (VANETs) can bridge the gap. VANETs are vehicular communication networks which are instantly and spontaneously established between Dedicated Short-Range Communication-enabled (DSRC) vehicles that do not need any infrastructure support. Hence, a fully distributed algorithm that can operate asynchronously in individual vehicles is necessary to decide on which cluster it has to join, whether it has to act as cluster head or gateway, etc. Road safety applications demand reliable delivery of warning messages to as many vehicles as possible that are approaching towards the zone so that the drivers can take necessary actions at the earliest moment. Though flooding is a simple technique to disseminate the messages to all vehicles, the broadcast storm problem [3] introduces network congestion and delays. Also in VANETs, because of the intermittent connectivity and network partitions due to fast-moving vehicles, providing a stable and reliable communications with high reachability becomes a major challenge [4; 5; 6]. For reducing the broadcast storm problem, a simple solution is to suppress the rebroadcast of the message to the extent possible without affecting the reachability of the message. Suppression of rebroadcasting can be achieved through selecting a limited number of next forwarders by grouping the vehicles into clusters and selecting the cluster heads and gateways in an efficient manner that ensures reachability. Hence, the research questions at hand are how to group the vehicles into clusters, how to select cluster head vehicle and gateway vehicles in a cluster in an efficient manner such that the number of rebroadcasting vehicles is reduced, but without reducing the reachability of the message. Vehicles are equipped with sensors for detecting the danger ahead or traffic congestion. Once a vehicle senses an unexpected event, it originates a warning message and disseminates it to the vehicles that are coming towards the zone. To disseminate the information in the wireless medium, broadcasting is a good choice. Among the broadcasting protocols, flooding is a simple network-wide broadcasting protocol [7] that has high reachability. However, it introduces a significant issue called a broadcast storm problem [3], since the vast amount of rebroadcasts results in network congestion. Though the increase in the number of rebroadcasts enhances the reachability of the message to all vehicles of interest, it increases the delay due to higher collisions and retransmissions as well. Hence, the number of messages transferred in the network should be limited to reduce the network delay and congestion. For further rebroadcast, a subset of vehicles that receives the alert message should be selected to control the broadcast storm problem. The selection of such vehicles is achieved by grouping (clustering) the vehicles based on topology, density, distance, speed, location or a combination of these [8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21].