This paper summarises a recently conducted study of the gap acceptance and capacity of roundabouts. The study had three principal objectives: (1) to examine further and to evaluate a previously developed model for determining the capacity values of entry into a roundabout intersection; (2) to estimate the gap size above which gaps are not relevant to gap-acceptance analysis at roundabouts; (3) to evaluate the gap-acceptance characteristics of drivers at a roundabout intersection as influenced by the waiting time on the minor approach leg. Video-taped data were collected at two relatively heavily trafficked roundabouts in Haifa and Ramat Hasharon (Israel); the data consisted of gaps, waiting times on the approach road, and circulating volumes. An entry-capacity model, developed by the authors in a previous study that evaluated capacities at six level sites, was tested further. It was found that the capacities of the roundabouts were generally consistent with the capacities that the previous model had predicted. However, at the Haifa site it appeared that an upgrade on the approach caused an increase in gap acceptance values. A model for determining the maximum relevant gap at roundabouts was developed and employed in the analysis to determine the critical gap. The waiting time prior to accepting a gap was found to have about a 5 percent impact on the critical accepted gap when the waiting times were near 25 s. An exponential model was calibrated to fit the impact of waiting times on the critical accepted gaps. (a).
Samenvatting