# 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
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Performance Dimension** & **Video Camera Technology** & **Millimeter Wave Radar Technology** & **ETC Multi-Sensor Fusion Technology** \\ \hline \multirow{2}{*}{System Architecture} & Network connection to host computer or cloud & Network connection to host computer or cloud & Cloud-based architecture with edge computing support \\ \hline \multirow{2}{*}{Detection Coverage} & Generally covers 3–4 lanes & Up to 12 bidirectional lanes & Implanted lane coverage capability \\ \hline \multirow{3}{*}{Core Detection Capabilities} & Vehicle identification & Target characteristics’ detection & Vehicle identity tracking \\  & Target characteristics analysis & Precise position coordinates & Position coordinate detection \\  & Visual evidence collection & Motion parameter measurement & Travel path reconstruction \\  & & & Multi-modal data integration \\ \hline \multirow{3}{*}{Environmental Adaptability} & Performance varies with lighting and weather conditions & High detection accuracy, independent of environmental conditions & High detection accuracy, independent of environmental conditions \\ \hline \multirow{4}{*}{Data Output Types} & Trajectory data (position, speed, vehicle type) & Motion parameters and target classification & Comprehensive traffic parameters \\  & Traffic flow parameters (volume, speed, occupancy, queue length) & Motion parameters and target classification & Vehicle identity and ownership information \\  & Traffic event detection (parking, speeding, lane changing, wrong-way driving, congestion) & Distance and position measurements & Historical transaction records \\  & & Basic traffic flow statistics & Cross-regional travel patterns \\  & & Basic traffic flow statistics & Small-target tracking (pedestrians) \\  & & & Enhanced event \\ \hline \multirow{2}{*}{Data Processing Architecture} & Data transmission to cloud & Data transmission to cloud & Supports both local processing \\  & Limited computing power and non-upgradeable hardware & Limited computing power and non-upgradeable hardware & Scalable edge computing with video analysis and sensor \\ \hline \multirow{2}{*}{Algorithm Flexibility} & Fixed, single-purpose algorithms & Fixed, single-purpose algorithms & Flexible multi-algorithm \\  & & & configuration with site-specific \\ \cline{1-1}  & & & training capabilities and \\ \cline{1-1}  & & & continuous optimization support \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of application effects of different sensing technologies. However, ETC applications in urban transportation still face several challenges. First is the coverage issue: although highway ETC adoption rates are high, coverage on urban roads remains limited. Second is the standardization issue: ETC applications in different cities and scenarios lack unified standards, affecting system interconnection and interoperability. Finally, data security and privacy protection issues have become important challenges as application scenarios expand, requiring a balance between data utilization and privacy protection. From a development perspective, ETC applications in urban transportation exhibit several important characteristics: First, the diversification of application scenarios, expanding from single toll collection functions to multiple domains including parking, transit, and logistics; second, deepening technological integration, with an increasingly deep fusion between ETC and technologies such as video, radar, and communications; third, intelligent service models, with intelligent services based on big data and artificial intelligence becoming the development direction; fourth, refined management approaches, with ETC data providing data support for refined traffic management. These development trends indicate that ETC technology is transforming from traditional toll collection tools to the important components of urban intelligent transportation systems, providing crucial technical support for constructing smart city transportation systems.