## 5 Conclusions  
UAV-enabled ITSs will be among the most radical advancements in future transportation systems. This paper provides an overview of the latest developments in various sectors related to the use of UAVs for ITSs, organized within a three-layered framework. The first layer of the UAV-enabled ITS framework focuses on the technical specifications of UAVs, which are crucial for effective integration into transportation systems. The design and specifications of UAVs must consider factors such as size, weight, maneuverability, flight time, and energy capacity. These factors influence the suitability of UAVs for specific ITS applications. Moreover, effective UAV deployment and trajectory optimization are crucial for maximizing their benefits in ITSs. This layer explores research on methods for optimizing UAV locations, trajectories, and communication networks to ensure efficient and reliable operation. The second layer of the framework comprises the communication networks between UAVs and vehicles and the responsive traffic monitoring system. Different types of UAV communication networks (UAVCNs) are discussed, and some network design considerations are identified. Additionally, the recent advancements, applications, and challenges in implementing UAVCNs are identified. The UAV-assisted vehicle ad hoc network communication architecture can provide significant coverage for traffic monitoring and efficient emergency services. However, implementing UAVCNs involves challenges such as maintaining reliable communication links, ensuring data security, and addressing potential interference. The third layer of the framework includes data collection and data processing methods that are essential for transforming raw data into actionable insights. UAVs offer significant advantages over traditional data collection methods, such as \"in situ\" technologies and floating car data (FCD), in terms of flexibility, cost-effectiveness, and coverage. UAVs can capture high-resolution traffic data from various perspectives, providing valuable information for analysis. Researchers have developed various data processing techniques for extracting traffic parameters from UAV-collected video data. These extracted traffic parameters can be used for vehicle detection, tracking, and traffic management. Moreover, state-of-the-art research developments and the applications of UAVs in the transportation sectors are also explored. The key areas include the role of UAVs in enhancing road safety, highway infrastructure management, emergency response, delivery services, and cybersecurity. This discussion implies that UAV technology has the potential to significantly impact the transportation sector by improving safety, efficiency, and sustainability. However, addressing the challenges and implementing appropriate policies and regulations are essential for realizing the full benefits of UAV-enabled ITSs. The most significant challenges for implementing UAV-enabled ITSs include ensuring security from cyberattacks and ensuring other forms of data protection, improving energy efficiency, and developing AI-driven algorithms. These areas need further research and development to fully utilize the potential of UAV-enabled ITS. Overall, this paper provides a comprehensive insight into the advancements and limitations of UAV technology in implementing ITSs, which will be beneficial in achieving robust ITSs in the future. Conceptualization, T.A. and N.Y.; methodology, T.A. ; validation, A.D., L.G.A. and N.Y.; formal analysis, T.A. ; investigation, T.A. ; resources, N.Y.; data curation, T.A. ; writing--original draft preparation, T.A. ; writing--review and editing, A.D., L.G.A. and N.Y.; visualization, T.A. and N.Y.; supervision, A.D., L.G.A. and N.Y.; project administration, N.Y.; funding acquisition, N.Y. All authors have read and agreed to the published version of the manuscript.