## 2 UAV-Enabled ITS Framework  
Future UAV-enabled ITSs could have various critical components significant for their successful implementation. To properly understand the step-by-step implementation of UAV-enabled ITSs, crucial components will be discussed using the three-layered framework shown in Figure 1.  
The first layer of the UAV-enabled ITS focuses on UAVs' technical and operational properties. It further involves the following three key factors: (1) defining UAV design and specifications to meet specific requirements, (2) optimizing UAV deployment to ensure maximum coverage and efficiency, and (3) analyzing UAV trajectory regulations for effective traffic monitoring.  
Figure 1: UAV-enabled intelligent transportation system (ITS).  
The second layer encompasses two main components. The first component is the communication networks essential to the ITS infrastructure, including vehicle-to-vehicle (V2V), vehicle-to-UAV (V2U), UAV-to-UAV (U2U), and UAV-to-vehicle (U2V) communications. These networks should also be connected to the Internet and cloud services for efficient data management and regulation. The second component is the responsive traffic monitoring system, which continuously monitors traffic flow and detects anomalies such as accidents, roadwork, adverse weather conditions, and rule violations [16]. The system is designed to respond promptly to these events to maintain optimal traffic conditions.  
The third layer of the framework focuses on data collection and processing. In addition to visual traffic data, other data types, such as infrared, light detection and ranging (LiDAR), radar, acoustic, and environmental data, can be collected using sensors and then transmitted to storage devices or uploaded to cloud servers. These data are processed to extract valuable traffic information that can provide comprehensive situational traffic awareness. The processed information can be used for further predictive analysis and decision-making to improve overall traffic flow.  
Additionally, cybersecurity must be integrated at every layer in this three-layer UAV-enabled ITS framework to ensure overall system integrity and safety. At Layer 1, technical specifications should include robust security protocols to protect the UAV's hardware and software from vulnerabilities. Layer 2, which encompasses the communication network, requires secure channels to safeguard data transmission between UAVs and ground control stations against interception or attacks. Finally, Layer 3 focuses on data collection and processing, where implementing stringent cybersecurity measures is essential to protect sensitive information and ensure the accuracy and reliability of data analysis. This comprehensive approach to cybersecurity helps create a resilient UAV-enabled ITS framework.  
Introducing the three-layered framework for UAV-enabled ITSs significantly advances existing research. This innovative approach provides a structured approach to the UAV-enabled ITS implementation process and offers holistic solutions that enhance scalability, efficiency, and real-time performance in ways that previous fragmented efforts have often struggled to achieve. Regarding scalability, the first layer discusses the UAV specification and requirements, facilitating a scalable model that can adapt to various urban environments and traffic scenarios. The second layer emphasizes efficient communication, directly addressing the limitations of conventional systems that frequently encounter delays and bandwidth constraints. Additionally, existing research often overlooks the complexities of real-time data analysis, leading to delays in decision-making. Therefore, the third layer of the framework should prioritize real-time processing capabilities, ensuring that traffic data can be swiftly analyzed and utilized for immediate decision-making. The three-layered framework serves as a structural means to cover various significant elements of the ITS.