An-Najah Staff

The use of crash data based methodologies for safety evaluation has been usually problematic due to the many shortcomings such as, unavailability and low quality of historical crash data. Other than crash data based analysis, development of micro-simulation models in conjunction with surrogate safety measures is shown to have potential to complement traditional safety analysis. However several previous works found that existing measures for the assessment of intersection safety such as post- encroachment time (PET), time to collision (TTC) and speed cannot each one alone represent the overall safety levels including crash probability and severity simultaneously. Thus, this study aims to propose a safety measure that considers crash probability as well as expected severity. By utilizing the change in the total kinetic energy before and after the collision, angle of collision and PET, the proposed conflict index is derived. Several videotaped signalized intersections in Nagoya City, Japan are utilized to extract vehicle trajectories through which conflict characteristics are estimated. The relationship between the estimated distributions of the proposed index and the records of severe crashes of the same sites are presented. It is concluded that the proposed safety measure is successful in providing a similar ranking of different signalized intersection to the ranking which is based on the number of crashes occurred at each site. The proposed measure can assess policy makers in prioritizing different sites for safety improvements projects.

The usage of traffic simulation to evaluate the safety of signalized intersections is an innovative approach to assess performances of various layouts or operations upon the safety of these facilities. This study presents the development of a microscopic simulation model aiming at the safety assessment of signalized intersections. This paper starts with a comprehensive discussion regarding the basic requirements for such a simulation model. The proposed simulation model integrates many key behavioral models of road users such as stop/go decision at the onset of yellow, turning paths, turning speeds, start-up response time and pedestrian gap acceptance models and so on. The main feature of these empirical models is that they consider the stochastic behavior of road users. Furthermore, they are sensitive to the layout and the operation of signalized intersections. This paper discusses how different conflicts are presented inside the simulation by demonstrating the mechanism of one of these conflicts. Model validation and a case study are conducted. The validation results show that the simulation model reasonably represents the conflict occurrence at signalized intersections, which proofs that such a model can be a reliable approach for the safety assessment. A case study is conducted to compare the performance of compact layout intersections with wide size ones. Trends of safety improvements are observed in the simulation results, although a generalized conclusion could not be made