An Analysis of Heavy Vehicle Impact on Roundabout Entry Capacity in Japan

AbstractHeavy vehicles behave differently from ordinary passenger cars due to their characteristics such as size and operational performance. At roundabout, entry capacity estimation mainly focuses on passenger cars. In HCM 2010, the impact of heavy vehicles on entry capacity is considered through a heavy vehicle adjustment factor fHV which includes heavy vehicle percentage and passenger car equivalent (PCE hereafter) value. It is generally set as 2.0, which means a heavy vehicle is assumed to be equivalent to two passenger cars. In existing methods, the PCE value at roundabouts is estimated based on several considerations such as entry capacity and move-up time. All of these considerations are influenced by local driver behavior and geometry conditions. Thus, this paper aims to estimate entry capacity considering the characteristics of heavy vehicle behavior in Japan. In this paper, characteristics of heavy vehicle behavior such as speed and gap parameters are firstly analyzed by using data observed at several roundabouts in Japan. Then, a simulation study which is calibrated based on the observation data is conducted by applying VISSIM 5.40. Roundabout entry capacity is estimated through assuming different heavy vehicle percentage values of each entry. Based on the estimated results of entry capacity, PCE value is calculated. The PCE values from the simulation study are compared with those values adopted by several design guidelines. Through the empirical analysis, it is found that heavy vehicles move in lower speed than passenger cars in the process of travelling roundabouts. The headways which are formed by heavy vehicles are commonly greater than those only formed by passenger cars. Then, PCE values which are calculated from simulation output are shown to change with different combinations of heavy vehicle percentage of each entry. The results in this paper provide a reference for roundabout entry capacity estimation considering heavy vehicle behavior in Japan. Future works are some further analysis from the viewpoint of geometry, since heavy vehicle behavior is significantly influenced by roundabout geometry such as inscribed circle diameter and circulatory roadway width, particularly at compact roundabout which is often the case in Japan