Utilization of Gaps at Single-Lane Roundabouts

Abstract

The study of gap acceptance behavior at roundabout entries is important for both capacity and safety analysis. Although considerable research exists on the relative size of vehicular gaps that are accepted during the driver decision process when entering a roundabout, the effective use of accepted gaps has not been adequately addressed. In the same way as follow-up time between entering vehicles is deemed to be a critical component in the entry capacity of a roundabout and considered in gap-acceptance derived capacity models, it is proposed here that the temporal distribution associated with when drivers enter into usable gaps is of equal importance. Approximately 60 hours of video were collected at six single-lane roundabouts located in Maine, New Hampshire, Vermont, New York, and Alaska, from which the gap decision processes of drivers were extracted and analyzed. A total of 1,181 accepted gaps were observed under saturated conditions and were included in the final dataset. The data show statistically significant temporal variations in the utilization of usable gaps by drivers, as well as between-site differences across the study locations. These findings suggest potential merit in the consideration of this factor in the calibration and capacity analysis process for single-lane roundabouts.