How to Use Traffic Safety Indicators for Freeway Safety Evaluations?

Traffic safety evaluation based on traffic conflict is a new method noticeable for traffic safety researchers. Traffic conflict is an observable interaction between two or more vehicles and can be calculated in various methods. In this paper, time-to-collision (TTC) as a microscopic traffic safety index is used in traffic conflict technique. Microscopic traffic data of I-80 freeway in NGSIM project has been used for analytical calculations. For different groups of traffic, parameters such as headway, spacing, leading and following vehicle velocities and leading and following vehicle types, TTCs have been calculated and then compared. Results indicate that traffic safety in lane 1, as HOV lane, is the highest. Also, vehicle following heavy vehicles have the smallest TTCs in percentage. It seems that traffic conflict technique makes new opportunities for traffic safety engineers to evaluate freeway safety without the need for freeway crash data.