ارزیابی ریسک خطر حرکات ترافیکی در ناحیه فیزیکی تقاطع بدون چراغ بر اساس شاخص TTC

The safety attracts attention increasing of traffic engineering to itself. The development of cities caused increasing of vehicles and accidents. The accident statistics show that the intersection points are one of the most eventful that occur 50 percent of all accident and 25 percent of human casualties. The first step in improving traffic safety is identification of hazardous situations. To improve traffic safety and design safety measures, It is important to recognize hazardous situations and causes of them. In addition, evaluating the effectiveness of measures implemented is also important. Based on traffic accident data, hazardous situations can be identified in roads and network. However, in small areas such as intersections, especially in resolution of maneuvers, identification of hazardous situations is impossible by using accident data for reasons such as the low occurrence of accidents in a particular area and record the exact location of the accident event. Due to shortcomings of traffic accident data, using surrogate measures such as traffic safety indicators have been taken into consideration. Therefore, in this study was used the traffic conflict. According to different problems of traditional traffic safety evaluation, the using of necessary methods is needed. In recent years, using of traffic conflict indexes has increased. Time-to-Collision (TTC) is one of the first and most widely used time-based indicators and many of the indicators are based on it. For using of these indexes the users’ speed, moving direction is needed. For high attention in safety evaluations and considering the type of the vehicle, two dimensional modeling of vehicle is presented. The critical interactions density index was based on the accident time index and traffic volume. The risk areas were identified three-dimensional by using ARC GIS software in the physical area of the intersection. By using this method, there is possible to identify high-risk areas based on critical traffic conflict. By using information obtained, determined how to improve intersection safety. As a case study the intersection of Vesal Shirazi to Bozorgmehr without traffic light in Tehran were selected. By video analyzing, data was recorded and risk areas were determined by using the method proposed in this paper. The evaluation results show that entry minor path to major path is riskiest because of conflict of the right movement minor path with the direct movement of the major path and the left movement minor path with the direct movement major path. The risk of right movement of minor path conflict to direct movement of the major path is 245.1 that about 8 times the average risk of all movements and , the risk of similar conflict on the other side of the intersection is 89.These conflict are the main reason for the increasing of the intersection risk.