Comparison of Time to Collision and Time Headway in Rear End Collision Avoidance Systems

The use of Intelligent Transportation Systems (ITS) has enhanced road safety. Most of Advanced Driver Assistance Systems (ADAS) as a subgroup of ITS، can prevent accidents by facilitating driving. Vehicle Collision Avoidance Warning Systems (IVCAWS)، as an ADAS، helps drivers to detect a potential accident. The most important point in IVCAWS development is to define an appropriate warning strategy، which alert drivers when he/she is really in danger and must have a reaction. Heretofore، two time-based safety indicators named، Time-to-Collision (TTC) and Time Headway (THDW) are used to activate IVCAWS to prevent rear-end collisions. In this article، these two indicators are compared، and a critical threshold for each one is determined to be used in IVCAWS. For this purpose، microscopic traffic data of I-80 freeway is used. Results indicate that، TTC’s critical threshold is usually about 1 to 2 second less than THDW’s threshold.