# Urban Traffic State Sensing and Analysis Based on ETC Data: A Survey
## 4 Traffic State Analysis and Assessment Using ETC Data
### Regional Traffic State Analysis  
Regional-level traffic state analysis requires the comprehensive consideration of interactions among multiple road segments and nodes, with complexity and systematicityfar exceeding the analysis of individual cross-sections or segments. Regional analysis not only requires processing large volumes of multi-source heterogeneous data but also demands an understanding of complex spatial correlation relationships and temporal evolution patterns. ETC data-based regional traffic state analysis technology achieves the comprehensive sensing and scientific assessment of regional traffic operational states by constructing systematic analytical frameworks. Regional congestion situation index construction represents the core technology for regional traffic state analysis. Constructing comprehensive indices reflecting overall regional congestion levels based on ETC data requires the comprehensive consideration of multi-dimensional traffic parameters and the establishment of scientific index calculation models. [PERSON] and [PERSON] constructed traffic operation analysis chromatograms based on Wuhan's ETC system [25], providing important technical references for regional traffic state visualization analysis. This research was founded on speed-flow models, comprehensively considering flow and speed indicators based on floating car and ETC river-crossing flow data, separately determining their classification standards. Based on this foundation, traffic operation analysis chromatograms were constructed, avoiding potential operational status misjudgments that might occur when employing single flow indicators. The application results from Wuhan demonstrate that these chromatograms can provide intuitive and powerful technical support for the real-time monitoring of road operational conditions, analyzing road anomalies, and quantitatively analyzing actual road capacity and free-flow speeds. The innovation of this research lies in achieving the intuitive expression of complex traffic states through chromatographic representation, enabling traffic managers to rapidly understand the overall regional traffic operational conditions. Compared with traditional digital indicators, chromatograms possess advantages, including strong intuitiveness, ease of understanding, and convenience for comparison, providing more user-friendly technical interfaces for traffic management decision-making. Inter-regional correlation analysis reveals inherent connections and mutual influences within urban transportation systems. Analyzing traffic flow correlations among different regions and identifying the source-sink relationships of traffic flows holds significant importance for understanding the overall operational mechanisms of urban transportation. Inter-regional correlations manifest not only in quantitative relationships of traffic flows but also in temporal synchronization, spatial continuity, and influence transmission across multiple dimensions. The vehicle identity tracking characteristics of ETC data provide unique data foundations for inter-regional correlation analysis. By analyzing vehicle flow trajectories among different regions, traffic connection intensity and directional characteristics between regions can be accurately identified. This analysis can not only reveal the spatial structural characteristics of urban transportation but also predict the transmission effects of traffic state changes between regions. The application value of inter-regional correlation analysis lies in providing scientific foundations for regional coordinated management. By understanding mutual influence relationships among different regions, coordinated and unified management strategies can be formulated, avoiding the poor overall effects resulting from local optimization and achieving the systematic optimization of regional traffic management.