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ُُDissertation Title
Using Surrogate Safety Measures for Safety Evaluation in Urban Intersections
Case Study
Dr. Hosein Haghshenas-Dr Mohammad Tamannaei


Urban intersections as bottlenecks of road facilities, have critical impacts on traffic serviceability. There are several parameters which can improve intersection operations. Safety is an important index which can be considered as a transportation indicator. Surrogate safety measures are categorized as proactive indices that can be utilized for safety assessment without any crash occurrences. Traffic conflicts are among such parameters which are risky situations of traffic movements. In this research, Azar intersection loacated in Isfahan, Iran, was assessed from different points of view. Afer simulation and calibration of the intersection in VISSIM simulation software, the most important traffic and safety parameters were evaluated. Subsequently, 117 scenarios in distict two, three and four phase states were defined. These scenarios were signalized in pre-timed state using highway capacity manual methods. After performing simulations, all trajectories were exported to SSAM software and each type of conflicts are determined. Finally, a linear regression model were obtained for each type of indicators and all the relevant parameters were determined. Consequently, it was determined that the ratio of average green times to cycle lengths is the most influencing parameter among all timing parameters. When this ratio increases, delays and all the conflict types except crossing conflicts decrease and crossing conflicts increase. Such equations can help planners to identify the best signal timing and phase plannings in accordance to different traffic states. Other important parameters in these models are related to traffic loads.





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