Measuring the Performance of Standard Two-Lane Roundabouts under Demand Uncertainty Using Monte Carlo Simulation Technique

Roundabout capacity is one of the most important features influencing the position of the roundabouts as traffic facilities. Many of the roundabouts that have been designed and implemented in the past, today are faced with capacity problems, so that in most cases they need to be redesigned. The appropriate operation of a transportation facility will be possible only when the demand and capacity are matched. In other words, in order to meet the exact demand, we need to create the appropriate capacity for facilities at certain levels of service. However, in real-world conditions, it is difficult to assume exact quantities of demand due to fluctuations over different periods of operation. In this research, the capacity of two-lane roundabouts has been analyzed with respect to demand variability. In order to consider the dispersion of demand, demand is considered as a uniform probability distribution function. The method of Highway Capacity Manual (HCM2010) has been used to determine the roundabout capacity. Monte Carlo simulation method is adopted to evaluate the control delay of the roundabout under demand variability. The results of this study show that, by increasing the variability of demand, the control delay will increase drastically, so that a high dispersion of entry volumes can make the level of service of the roundabout two times less compared with when the demand is constant.