Effect of Pedestrian Impedance on Vehicular Capacity at Multilane Roundabouts with Consideration of Crossing Treatments

Past research has documented that pedestrian crossings at modern roundabouts can result in an impedance effect on the available capacity of entering traffic. The magnitude of this impedance effect is intuitively linked to the allocation of rights-of-way at the crosswalk, where a greater likelihood of driver yielding is expected to affect capacity more severely. However, existing pedestrian impedance models in the 2010 Highway Capacity Manual and the FHWA Roundabout Guide are not sensitive to yielding rates. The principal objective of this paper is to quantify pedestrian impedance effects on the vehicular entry capacity at multi-lane roundabouts as a function of driver yielding behavior. A calibrated microsimulation model is used to develop the relationships and explore changes in volume and yielding parameters. Impedance models are further developed for the pedestrian hybrid beacon (PHB) treatment, which is gaining increasing attention at multi-lane roundabouts across the United States. The results confirm the expected effects that the pedestrian impedance is more severe with higher pedestrian flow rates but decreases in severity with greater conflicting flows. The results further show that the effect of varying yielding rates on the impedance effect is minimal for congested roundabout approaches, because the relative effect of yielding is small compared with that of pedestrian volumes and conflicting circulating flow. The analysis of the PHB treatment shows that the impedance effect of the same pedestrian flows is generally less than that for an unsignalized crossing environment.