# Evaluating the Impact of Drone Signaling in Crosswalk Scenario
## 2 Related Work
Reference [22] proposed UAV-assisted vehicular ad-hoc network (VANET) routing protocols to improve data routing and connectivity among ground vehicles through the use of drones. Several researchers have been more particularly interested in the interaction between drones and cars and suggested the development of hybrid ad-hoc networks. In Reference [23], authors proposed an infrastructure-less Vehicle-Drone hybrid ad-hoc network (VDNet), where UAVs are expected to boost V2V data message transmission. Authors in Reference [24] investigated the use of an heterogeneous network of drones and vehicles in an urban context, where communications between drones and vehicles may be crucial for transmitting important information, such as real time traffic. [PERSON] et al. tackled different aspects of the communication between cars and drones. In Reference [25], they proposed an experimental characterization of UAV to Car communications and emphasized that its range could reach 3 km in a rural area, when the 5 GHz frequency band is used. In Reference [26], they proposed a realistic model for simulating this type of communication link, enabling alert broadcasts in emergency situations. In Reference [27], they have recently developed a technique to optimize the UAV positioning in a 3D space, for dynamic Drone to Car communication. One can find more information about open problems and remaining challenges in the field of UAV communications in Reference [28]. Another C-ITS feature is that vehicles are expected to be autonomous (no human intervention is needed). Hence, road safety is an important aspect that should be considered and highlights number of issues that are still open problems, especially when Vulnerable Road Users (VRU), such as pedestrians, cyclists, or two-wheel-vehicles, are involved. As far as road safety is concerned, authors in Reference [29] surveyed communications between vehicles and VRUs and suggested that an open research challenge in the area is that a vehicle and a VRU that are potentially on the verge of collision may need to communicate with each other using real-time algorithms in the presence of V2X communications. In addition, drones can be a viable technology for monitoring pedestrian traffic characteristics in outdoor pedestrian zones [30]. UAVs are also used as aerial sensors to collect videos aiming at analyzing surrogate safety of pedestrian-vehicle conflicts at intersections [8]. In Reference [31], authors tackled pedestrian safety diagnosis at signalized crosswalks using traffic conflict technique, and emphasized that the most serious pedestrian-vehicle conflicts occur when vehicles travel at high speed. Tracking and simulating pedestrian movements is part of the solution to protect their safety at intersections [7]. In Reference [32], the reader can also find models for pedestrian path prediction at 2 s time horizon, and this helps to analyze interactions between pedestrians and straight-going vehicle at non-signalized crosswalks. Extensive research studied pedestrian behaviors, while other works focused on the car driver behavior, like the recent patent [33] where the inventor proposed a traffic control system, controller, and method for directing vehicle behavior at a defined spatial location, based on a UAV hovering above a roadway. Analyzing the vehicle driver behavior is of interest not only to avoid collisions with other road users but also to reduce gas emissions and their impact on the environment. This trend is related to climate change issues, especially in crowded cities. Extensive research works tackled the aspect of energy consumption minimization. In fact, based on the Pulse Width Modulation (PWM) dimming principle, authors in Reference [34] presented a partial feed-back closed loop control scheme for LEDs, which has the capability to stabilize illuminance satisfactorily and which calculates economically the quantity of electric light to compensate the illuminance. Authors in Reference [35] showed that the driver behavior has a direct impact on the environment and the vehicle emission.