From Structural Equation Modeling to Macroscopic Fundamental Diagrams: Investigating the Impact of Road Segments Safety on Network Level Efficiency

The main objective of this research is to expand upon the link between network flow (mobility) and safety through the estimation of Macroscopic Fundamental Diagrams (MFD) and Structural Equation Models (SEM) with different levels of disruptions caused by different surrounding driving conditions. Analysis begins with the aggregation of microscopic level loop detector data and collision data provided by The Korea Expressway Corporation (KEC). The KEC operates highway tolls throughout South Korea and continues to expand upon the nearly 4000 km of high-speed motorways it provides. The rich, detailed collision and traffic flow data collected on these roadways makes the region an ideal candidate for the new analysis technique that is presented in this study. Three specific types of nonrecurrent disruptions, as suggested by SEM results, (inclement weather conditions; increased holiday demand; increased number of collisions) are analyzed and compared in this study. By estimating and comparing MFDs for these specific cases, the differences in network level disruptions caused by these events are visualized, quantified and discussed. Additionally, by using SEM to quantify the impact of these disruptive events on safety and impedance at the link level, spatial and temporal analysis can be conducted – establishing a link between the microscopic event-based data (mainly collisions) and the macroscopic network performance measures of safety and traffic mobility.