# Evaluating the Impact of Drone Signaling in Crosswalk Scenario
## 2 Related Work  
For more than twenty years, many research works have investigated the potential of drones in traffic monitoring scenarios. Collected data from drones flying in urban environment are used for a wide range of applications [9], such as evaluating the real traffic flow conditions in urban areas [10]. In a first survey [11], the authors highlighted how aerial monitoring has the potential to yield detailed information to help traffic planners. In a second survey [12], the authors listed UAV-based systems for traffic monitoring and research trends in the area. References [11; 12] mentioned extensive efforts to carry UAV-based systems for traffic monitoring in universities (California, Ohio, Florida, etc.) and research centers. [PERSON] et al. [13] developed a security situational aware intelligent traffic management using a UAV that gives decision commands for routing or shortest traffic paths. Then, in Reference [2], a universal guiding framework for ensuring a safe and efficient execution of UAV-based traffic studies has been proposed. More recently, some patents have been submitted to design particular UAV structures able to meet efficient traffic monitoring purposes. As an example, Reference [14] deals with a system of two drones: a surveillance drone based on the recognition of difficult situations on fast road lanes, and a signaling drone which makes decisions to display the most relevant signaling messages on a LED-based variable messages panel. In addition, the interest to Cooperative Intelligent Transportation Systems (C-ITS) has risen in recent years, especially in the context of smart cities. Authors surveyed major techniques and solutions for both signalized and non-signalized cooperative intersections [3]. [PERSON] et al. developed and constructed an adaptive street light system that improves safety at intersections with a focus on rural intersections, which have an elevated number of road accidents [15]. In C-ITS systems, thanks to Vehicle to everything (V2X) and everything to Vehicle (X2V) communications, both drivers and traffic managers share the information and cooperate to coordinate their actions to ensure safety, traffic efficiency, and environment preservation. Authors surveyed the concept of V2X, as well as the standardization techniques presently in use for communication by describing V2X applications, requirements, threats, and solutions. They have focused on the required initiatives for understanding the importance of V2X security in vehicular communication [16]. In addition, the integration of block chain, as a strong security mechanism, in next-generationV2X communications was examined, which comes up with new opportunities to empower advanced V2X networks, capabilities, applications, and services [17]. UAV can be used in a lot of ITS applications, thanks to the development of UAV-based systems. For example, [PERSON] et al. presented an emergency radio beacon specifically designed to find and recover small UAVs. They carried experiments to show its high precision and endurance [18]. According to Reference [4], UAV can be used in a lot of ITS applications, and there are huge potential and numerous challenges for UAV-enabled ITS for next generation smart cities. One among these challenges is UAV communications in smart cities. In Reference [19], the author developed algorithms and mathematical frameworks to design, optimize, deploy and operate UAV-based communication systems. In fact, UAVs can act as intermediate relays to collect information and transmit it to ground vehicles, due to their flexible mobility, especially if the communication ground infrastructure is not available [20]. The work in Reference [21] highlighted the minimum number of UAVs needed to guarantee a target connectivity threshold among vehicles, for a given geographical area and vehicle density, especially in the case of road side unit (RSU) failure and lack of Vehicle-to-Vehicle (V2V) communication.