A Superposition Assessment Method of Road Crash Risk and Congestion Risk: An Empirical Analysis

In road transport systems, various traffic risks in certain condition could produce joint actions, which increases the complexity of traffic risk assessment. Previous single risk assessment fails to reflect the superposition effect of multi-type traffic risks, so the result may underestimate or overrate the total risk strength of transport system. To address this problem, a novel risk assessment perspective that aims to evaluate the superposition effect of several traffic risks is studied. In this study, the risk quantification and standardization for single traffic risks is conducted first. Then a GARCH-VaR model is developed to explore the superposition impact of these single traffic risks. The GARCH-VaR model integrates the VaR theory and GARCH model, from which the superposition traffic risk is obtained by assigning every single traffic risk a reasonable weight. Finally, an improved k-means clustering algorithm is proposed to classify the superposition risk level. Empirical results demonstrate that the superposition risk of crash risk and congestion risk is lower than a single traffic risk in certain condition, which attributes to the weak interactions between various traffic risks. This finding illustrates the superposition risk does not necessarily go up with the increase of the risk category. Then the superposition risks are classified into high-risk level, moderate-risk level, and low-risk level, among which the classification accuracy of high-risk level is 92.85%-95.23%. The proposed method provides a theoretical reference for collaborative assessment of multi-type traffic risks, and the results could be potentially used in the comprehensive management of traffic risks.