Optimal transport network design for both traffic safety and risk equity considerations

Abstract

Traffic safety planning is one of the most cutting-edge research directions, which regards traffic safety as the main indicator of sustainable transportation. Although traffic safety has been widely recognized, it is rarely considered during the transport network design stage. Moreover, traffic safety performance usually refers to the total number of traffic accidents while the risk equity issues are given much less attention by transportation planners and managers. In this paper, a novel bi-objective bi-level model framework is formulated that explicitly captures the leader-follower nature of the relationship between authorities and travelers. In the upper-level, authorities design transport network by optimizing the impact of investment in terms of both total risk and risk equity. In the lower-level, a sequential four-step model with feedback is formulated to represent travelers' behavior responds to transport network design. The feedback procedure can converge to transport system equilibrium that is further fed back to the upper-level to measure network safety performances. To solve the proposed bi-level model, an efficient algorithm, named Dirichlet allocation algorithm, is designed on the basis of Dirichlet distribution, Method of successive averages (MSA), Frank–Wolfe algorithm and Dijkstra's algorithm. A simulated example using Nguyen-Dupuis network is conducted to verify the effectiveness of the proposed methods. The results show that transport network design has a great impact on traffic safety performances. The optimal network design can reduce traffic accidents and improve risk equity significantly from very beginning. The modeling framework can be a valuable tool for active safety planning. It provides valuable implications for network designers on how to design transport network for traffic safety and risk equity simultaneously.