New Model for Estimating the Influence of Pedestrians on the Entry Capacity of Roundabouts

The capacity of roundabout entries and exits can be significantly influenced by crossing pedestrians. To analyze this effect, an extensive microscopic simulation calibrated with empirical findings from field measurements at five single-lane roundabouts in Germany was conducted. The results revealed that the entry capacity adjustment factors used in the U.S. Highway Capacity Manual and the German Highway Capacity Manual do not sufficiently account for the capacity reduction resulting from crossing pedestrians. The results confirmed neither the convex shape of the adjustment factor functions nor the total extent of the capacity reduction. Thus, a new model was derived using gap acceptance theory. The new model accurately estimated the capacity reduction from conflicting pedestrians. The model used the entry capacity function as an input parameter and is therefore applicable for any type of roundabout. Furthermore, local boundary conditions like the blockage time of a single pedestrian, the grouping of pedestrians, and yielding behavior were considered as individual input parameters and could be modified by field measurements if needed. For all parameters, reasonable defaults were given. The new model has been derived in a way that it can be directly incorporated into existing quality-of-service assessment procedures to determine appropriate entry capacity adjustment factors. Moreover, the model could be extended to consider crossing bicycles simultaneously and is also valid for calculating the influence on the exit capacity.