## 1 Introduction  
Thus far, many studies and simulations to realize connected car technology have been actively conducted [1; 2; 3]. Connected car technology based on vehicle-to-everything (V2X) communication must be connected to other vehicles, objects, and people, but is composed of partially connected subgroups according to temporal and geographical influences such as time, location, and wireless network coverage [4]. If such a subgroup is not configured, all vehicles will broadcast messages containing their state such as vehicles' information, driving record, and path history every 10 microseconds according to European Telecommunications Standards Institute (ETSI) recommendations [5]. However, when such a broadcasting is executed, serious problems such as the broadcast storm [4; 6], message flooding [7], or message contention occur [8]. To solve these problems, most studies had been proposed and implemented vehicular ad-hoc networks (VANET)-based message dissemination, message multi-hopping, and message relay algorithms [9; 10]. [PERSON] et al. not only classified and reviewed some recent contributions to emergency message dissemination in vehicular networks but also discussed various proposed methods for emergency message dissemination based on the Intelligent Transport System (ITS), Internet of Things (IoT), Priority messaging, Clustering approach, Software-Defined Network (SDN), and Fog computing [9]. The work in Reference [4] studied the integration of emergency messages for connected cars. [PERSON] et al. proposed a real-time solution for traffic management by calculating the density of traffic on the roads, and high priority is given to a lane where emergency vehicles can travel [11]. The mechanism introduced by Reference [12] includes a smart real-time traffic monitoring system that monitors traffic statistics on a daily and weekly basis and works on early detection of an incoming emergency vehicle. [PERSON] et al. presented an approach for smart cities by integrating the concept of IoT and VANET to control the traffic lights and ease the movement of ambulances in cities [13]. In Reference [14], [PERSON] et al. introduced a dynamic scheduling algorithm for traffic signal timing. [PERSON] et al. proposed a protocol based on the position for broadcasting emergency messages in VANETs, and the disseminated messages are broadcasted to reduce road accidents [15]. The scheme of multi-hop clustering-based emergency message dissemination (MC-EMD) introduced by Reference [16] makes clusters of different neighboring vehicles, and the messages are sent to all clusters that are a bit far from the risk zone to avoid both network and traffic congestion. In Reference [17], the authors carried out performance modeling for emergency message dissemination using priority in VANET. [PERSON] et al. proposed a multi-hop message broadcast scheme, so-called the trinary partitioned black-burst-based broadcast protocol (3P3B), for time-critical emergency services in VANET [18]. In addition, there are many papers that present emergency message dissemination schemes based on congestion avoidance in VANET [19; 20; 21]. On the other hand, in non-line-of-sight (NLOS) situations, critical traffic situation information from the preceding vehicles needs to be transmitted to the following vehicles in order to avoid accidents. In cases of emergency situations such as traffic accidents involving preceding vehicles, having the preceding vehicles transmit the emergency message with priority to the following vehicles is the best approach to prevent secondary accidents. However, there are few studies to distinguish between vehicles in front of or behind the current vehicle, even within a subgroup of connected cars. [22; 23]. Studies on the changes in the dynamic topology due to frequent overtaking caused by variations in the speeds of vehicles are also scarce.