## 2 Literature Review
### Road and Traffic Awareness Approach  
In [19], the authors proposed a Multi-metric Geographic Routing (M-GEDIR) algorithm to select the next hop. The next node vehicle is selected from the dynamic forwarding region based on the probability of the area being safe or unsafe. It is a V2V communication where the roadside unit is not considered. This is an unrealistic approach as the processing time is long to determine the optimal path. In [20], a mechanism was developed based on a combination of the intersection-based routing technique with the shortest path-based traffic light-aware routing protocol. The protocol was named Reliable Path Selection and Packet Forwarding Routing Protocol (RPSPF) by authors. Data packets are transmitted based on the traffic patterns and the traffic light signals along the intersection. The protocol could provide a high delivery ratio and throughput but has connectivity issues like the end-to-end connectivity among vehicles will be broken when one node goes away, leaving the network. Thus, vehicles should reconnect to communicate. In [21] an efficient Parked Vehicle Assistant Relay Routing (PVARR) algorithm was proposed to guarantee vehicle-to-vehicle communication in VANETs. Based on this algorithm, practical cooperation between stationary and moving vehicles prevents the network from having broadcast storms, increases resource utilization rate, and effectively diminishes load on the network. Results prove that the packet delivery ratio for the proposed protocol is high. This mechanism does not use RSU as intermediate nodes while the communication is rather running through parked vehicles in that network. Having parked vehicles on the road, particularly highways, is not always common, and therefore this protocol is not applicable if no parked vehicles are available on the road. On the contrary, using RSU can reduce the number of hops (because there is a range for each RSU), which simultaneously reduces the delay when compared to parked vehicles. To enhance geographical source routing (GSR) protocol, research [22] proposed an efficient GSR (EGSR). This protocol has been designed mainly for urban areas, and it is assumed that every node in the network is equipped with a GPS and digital map. Additionally, it is assumed that the clocks of all nodes are synced. The proposed protocol uses the ant-colony algorithm to find the optimum path between nodes in the network. Each node can calculate the weight of the road segments by a small packet called ANT, which is generated by vehicles at the intersections. Based on the weight of every road segment, the sender selects the best road route to the destination. The road segment is constituted by distance and the delay between intersections. This protocol relies on the delay, which requires an accurate synchronization to be calculated. In addition, routing tables are updated using ANT packets generated in a timely fashion based on a constant value of \(t_{ant}\). When \(t_{ant}\) is short, routing overhead load is high, causing network instability and performance degradation. In [23], it was introduced a new mechanism called Distance and Direction based Location aided routing (DD-LAR), which is an extended version of the existing Directional-Location Aided Routing (D-LAR) Protocol. In this protocol, the sender node first checks for the locational information of its nearby neighboring nodes in the request zone within its transmission range. The neighboring node that is positioned at the minimum angular deviation and a maximum distance from the sender node will be selected as the next-hop forwarding node. However, in case of having a conflict in which the node has the minimum angular deviation while not having the maximum distance, then the algorithm prefers the previous version because the relative distance of all the nodes from the source node is negligible. Moreover, the previous version (D-LAR) gives a better hop count in a dense environment like the city traffic conditions. In [24], the authors proposed ISR protocol.