Impact Analysis of Headway Distribution on Single Lane Roundabout Entry Capacity

摘要

The Highway Capacity Manual (referred to as the HCM hereafter) 2000 model estimatesroundabout entry capacity under an assumption of circulating headways following anexponential distribution. However, some studies indicated that the HCM 2000 model couldover- or under-estimate entry capacity. This situation might be attributed to an unfitassumption of headway distribution type. Therefore, this study begins with analysis ofheadway distributions based on field survey. This study firstly indicates that the inverseGaussian distribution is the best fitted distribution type of headway samples. According tothis finding, we thus intend to adjust the HCM 2000 model. To this end, we propose asimulation based approach to estimate entry capacity of single-lane roundabouts. A linearrelationship is established to represent the relationship between a capacity ratio of thesimulation-based approach to the HCM 2000 model and conflicting flow. The linear functioncan be considered as a coefficient of the HCM 2000 model. It is believed that the modifiedHCM 2000 model outperforms the HCM 2000 model.