Abstract
Over the past decades many models for roundabout capacity have been proposed. Attention to this research sector has never stopped and still today new formulations are always being studied, especially in view of their direct application in design practice. This paper reports the first noteworthy results of a research concerning the Modified Chumanov (MC) model, which can be used to estimate the capacity of single-lane roundabout entrances. After a detailed examination of the original model recommended by the Russian guidelines for small urban roundabouts, the paper proposes some extensions which allow using the revised model even for larger intersections. The MC model also includes some parameterizations that allow its application with different road pavement surface conditions (i.e., dry and wet conditions). The MC entry capacity model, as function of circulating flow and other parameters dependent on geometry and environmental conditions, was compared with 15 widespread models considering a typical medium-sized single-lane roundabout. A validation test was carried out considering four capacity–circulating flow datasets from the literature. The proposed MC model showed good flexibility in adapting to data. This flexibility appears better than the most recent models by Highway Capacity Manual, in the absence of local calibration of the psychotechnical parameters.
Highlights
Capacity estimation is a fundamental issue in transportation systems analysis, as its values describe the maximum throughput of traffic demand that can be accommodated under current operating conditions
Are intimately related to Level of Service (LOS) assessment, a widespread approach for the description of the performances that a transportation facility is able to ensure for users
Queue and delay evaluations for unsignalized intersections resort to heuristic models for the time-dependent queue, which allow analyzing the whole range of situations that can occur in the real cases
Summary
Capacity estimation is a fundamental issue in transportation systems analysis, as its values describe the maximum throughput of traffic demand that can be accommodated under current operating conditions. In highway engineering, this is a crucial aspect regarding roadway segments and intersections. The coordinate transformation method [3], makes time-dependent queue formulas available for stationary and non-stationary condition treatment, i.e., for non-congested and congested traffic, respectively [4] From this point of view, capacity is the key variable as it reflects the queue discharge rate [5]
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