Seyed saber naseralavi - Assistant Professor, Shahid Bahonar University of Kerman, Iran
Hamed Nazari - M.S. Transportation planning, , Shomal University of Amol, Iran /Assistant Professor, Shahid Bahonar University of Kerman, Iran
Amir Izadi - Assistant Professor, Shomal University of Amol, Iran
Seyed Mohsen Sarabi - M.S. Transportation Planning. Shomal University of Amol, Iran

Driver rehearse and Failure to detect unsafe moments in the car-following Process, cause nearby locations to the collision and rear-end accidents. Collision avoidance warningsystems such as IVCAWS, to aim recognize unsafe moment in car-following situation, can reduce the risk of human's error and the accident occur. IVCAWS utilizes surrogate safety index to aware unsafe moment in car-following situation. Therefore the ability of thissystem to declare unsafe state, directly depends on safety indicator's capability. Already time to collision (TTC) and the headway (THDW) indexes have been proposed as theunsafe moment Detection indexes. To choose the Appropriate index detecting unsafe moment in rear-end collision warning systems, introducing of DRAC, PSD, THDW, TTC, MTTC as the most famous indexes in car-following safety studies was done in this research.Furthermore, considering the critical threshold and developing concept of total below the critical times for each of indexes, the relationships between indexes and warning unsafecapabilities of each indexes using real data to the traffic's micro flow would be evaluated. Results Analysis for each indexes on the I-80 Partial data of freeway traffic NGSIM project show that PSD, TTC and DRAC indexes have not be able to detect many dangerous moments. While the usage of THDW index involves high warning dangerous moments and drivers mistrust. But MTTC index having comprehensive scenario and real situations, shows the higher ability to detect unsafe moments. Hence the using of MTTC index in IVCAWS systems, causes improvement in performance and efficiency in these systems.

surrogate safety index, rear-end collision, unsafe moment, Collision Avoidance System