Globally, the modern roundabout is a common form of intersection control. While their use in the United States has increased, much work is needed in developing design guidelines and standards. One such area is highway-railway at-grade crossings (crossings) within, or in close proximity, to roundabouts. This paper attempts to determine the time required to clear a queue of vehicles on the approach of a single lane roundabout in the same manner as a track clear green interval at a signalized intersection equipped with railroad preemption. The 2010 Highway Capacity Manual (HCM) and Tanner-Wu models for capacity are presented and their results are evaluated against results obtained from microscopic traffic simulation. Results show that the Tanner-Wu model predicted the simulated track clearance times more accurately than the HCM model for clearance distances ranging from 60 to 200 feet in length. Furthermore, the Tanner-Wu model track clearance times were within five seconds of the simulated values for circulating flows below 1200 passenger car equivalents per hour.
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