COMPARATIVE ANALYSIS OF CRITICAL HEADWAY ESTIMATION AT URBAN SINGLE-LANE ROUNDABOUTS
According to models commonly used in practice, the capacity of roundabouts largely depends on the value of critical headway. The value of critical headway depends on the characteristics of vehicles, driving conditions, and geometric characteristics of intersections, but also on driver behaviour. Driver behaviour is the result of many factors that depend on the influence of the local environment, driver habits, mentality, etc. Accordingly, to calculate the capacity of roundabouts within the operational and planning analyses of roundabouts more accurately, it is necessary to use data that correspond to local conditions. In this paper, the critical headway was estimated at five urban single-lane roundabouts using five methods: Harders’, Logit, Raff’s, Wu’s, and the maximum likelihood method. In order to determine which of the stated methods provides the most realistic estimate of critical headway, a comparison of field capacity values with theoretical capacity values was performed. Based on the comparative analysis performed in MATLAB, as well as the calculation of percentage prediction error, it was found that the Harders' method provides the most accurate estimate of critical headway at observed roundabouts in two cities in Bosnia and Herzegovina. Due to the similarity in the design of roundabouts and driver behaviour, the results obtained in this paper can be applied in the surrounding countries, i.e., Southeast Europe.
critical headway; field capacity; conflicting flow rate; urban single-lane roundabouts