Investigation on entry capacities of single-lane roundabouts

Bothheavy goods vehicles (HGV) and exiting vehicles can significantly affect the entry capacity of a roundabout. However, their effects have not been taken into account in HCM 2000 model.Recently two studies have been carried out to address this issue: 1) Dahl and Lee (2012) proposed an expectation theory based approachto incorporate the effect of HGVs [1]; and2)Qu et al. (2013) deriveda new roundabout capacity model by assuming that each exiting vehicle could provide one entry opportunity for waiting vehicles [2]. In this paper, the two models are integrated using a scenario-based approachtoanalyse the effects of not only exiting vehicles but also HGVs. A comparative study indicates that HCM 2000 model performs well under low to mid traffic conditions while it underestimates the capacities under high traffic conditions in combination with high proportions of exiting vehicles.