# Urban Traffic State Sensing and Analysis Based on ETC Data: A Survey
## 2 ETC Systems: Historical Development and Current Applications
### Current Application Status of ETC in Urban Transportation  
With the successful application of ETC systems on highways, their application in urban transportation has gradually expanded, showing diversified and integrated development trends. The complexity of urban transportation environments poses new challenges for ETC technology while providing a greater scope for functional expansion. [PERSON] pointed out in her research that ETC systems play important roles in improving traffic efficiency, promoting multi-departmental coordination, and innovating service models in intelligent transportation [12]. This perspective accurately summarizes the core values of ETC technology in urban transportation applications. Unlike the relatively simple application scenarios on highways, the diversity of urban transportation requires ETC systems to possess stronger adaptability and scalability. The deep application of ETC + parking scenarios represents an important direction for urban transportation intelligence. Parking facilities at airports, hospitals, shopping centers, and other locations have introduced ETC contactless payment, achieving non-stop rapid passage and significantly improving user experience and operational efficiency. [PERSON] et al. designed an intelligent parking management system based on ETC technology, achieving unmanned parking management through system integration and significantly improving parking management efficiency and user satisfaction [13]. The success of this application model demonstrates that ETC technology has enormous application potential in urban static traffic management. The integrated application of ETC + transit systems embodies the technical implementation of public transportation priority development strategies. Applying ETC technology in bus lane management and transit signal priority enables precise vehicle identification and priority control, improving transit operational efficiency. Some cities have begun piloting ETC applications in transit vehicle management, achieving transit vehicle priority through coordination with signal control systems. The parallel vehicle networking concept proposed by [PERSON] et al. provides a theoretical framework for the deep integration between ETC and transit systems [14]. The intelligent management of ETC + logistics and delivery demonstrates the application value of ETC technology in freight transportation management. Utilizing ETC technology for truck passage management, route monitoring, and transportation optimization not only improves logistics efficiency but also provides effective means for urban freight management. [PERSON] et al. studied the innovative applications of ETC in multi-scenario applications, particularly emphasizing the important role of ETC technology in addressing pain points such as cumbersome payments and inefficient management in urban transportation, parking, and refueling processes [15]. The emergence of multi-source data fusion trends marks the evolution of ETC applications toward higher levels. Increasingly more projects adopt \"ETC+video+radar+MEC\" multi-source fusion sensing solutions. Compared to single video surveillance or microwave radars, multi-source fusion provides higher detection accuracy and anti-interference capabilities. Fusion sensing solutions accomplish vehicle identity identification and positioning, multi-target collaborative tracking, and traffic anomaly event determination through data cleaning, coordinate transformation, feature extraction, and structured fusion based on toll data and multi-source sensing. This trend of technological fusion indicates that ETC is evolving from a single identification technology to a comprehensive sensing platform. Table 1 summarizes the comparison of different sensing technology application effects.