## 2 UAV-Enabled ITS Framework
### Second Layer: Communication Networks for Traffic Monitoring
#### 2.2.2 Advances in Traffic Monitoring
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**References** & **Research Area** & **Methodology** & **Findings** \\ \hline [PERSON] et al. [48] & UAV-aided traffic monitoring systems & A systematic review of UAV-based traffic monitoring strategies & A universal multistep traffic monitoring framework. \\ \hline  & & Review of studies and applications incorporating unmanned aircraft systems (UASs) in transportation & Reveals current issues and emerging challenges. \\ \hline  & & & \\ \multirow{2}{*}{[PERSON] and [PERSON] [50]} & Big data-based traffic congestion analysis & Investigating traffic congestion by creating an extensive data repository of UAV-based traffic stream data & Offers an opportunity to test traffic models developed from diverse disciplines. \\ \hline [PERSON] et al. [12] & Adaptive multiple UAV-aided real-time traffic monitoring system & Adaptive trajectory-based multi-UAV & Better coverage rates and event detection rates. \\ \hline [PERSON] et al. [51] & General UAV-based traffic monitoring with cloud processing & Cloud processing and UAV-based traffic monitoring & Monitors traffic with high accuracy and flexibility. \\ \hline [PERSON] et al. [52] & Traffic monitoring based on UAV scheduling problem & Scheduling of UAV routes under uncertain demands & Competitive performance from a local branching-based solution method. \\ \hline [PERSON] et al. [6] & UAV-based smart traffic monitoring & \multirow{2}{*}{SG technology and UAV-based traffic monitoring} & Better projection of the number of accidents. \\ \hline  & & & \\ \multirow{2}{*}{[PERSON] [53]} & Cooperative traffic monitoring for drivers & UAVs collect and share vehicle data with other vehicles & Cooperation is an effective tool for traffic monitoring. \\ \hline [PERSON] and [PERSON] [54] & Rapid monitoring with a high-quality digital elevation model & UAV-based rapid aerial mapping system & The rapid traffic monitoring system successfully passes the integration test. \\ \hline [PERSON] et al. [55] & Developing technologies for autonomous UAVs operating over large-scale transportation networks & Multidisciplinary basic research & Requires multidisciplinary research competencies. \\ \hline  & & & \\ \multirow{2}{*}{[PERSON] et al. [56]} & Wallenberg Laboratory for information Technology and Autonomous Systems (WITAS) UAV project & Customization and incorporation of the network and requirements of the UAV platform & Presents research work by the computer vision laboratory at Linkoping University (LiU). \\ \hline  & & & \\ \multirow{2}{*}{[PERSON] et al. [57]} & Autonomous UAV-based system to track traffic on a road network & \multirow{2}{*}{Patrol, isolation, capture, and delivery–four-phase approach to monitor and detect intruder vehicles by cooperatively using UAVs and unattended ground sensors (UOSs)} & Demonstrates autonomous decision-making of cooperative UAVs and UCS. \\ \hline  & & & \\ \multirow{2}{*}{[PERSON] et al. [58]} & Development of an open-source software framework named UxAS & A software framework for autonomous UAV-based systems & Facilitates the development of new autonomous UAV-based systems. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Research summary on advances in traffic monitoring using UAVs. Short-term traffic monitoring using static solution methods is limited by a lack of flexibility, expensive sensors, and low coverage. To overcome these limitations, [PERSON] et al. [51] presented a general UAV-based traffic monitoring system using an onboard camera to record traffic flow information. The UAV-collected video data were then uploaded to a cloud server, where vehicles were detected from the video data using the Haar cascade algorithm and tracked using a frame-by-frame comparison algorithm. The experimental results demonstrated that the proposed traffic monitoring system is highly accurate and flexible. [PERSON] et al. [52] investigated real-time traffic monitoring systems from the perspective of UAV scheduling problems with uncertain demands.