Using Simulation to Plan Capacity Models by Lane for Two- and Three-Lane Roundabouts

Recently, capacity models have been developed for single- and double-lane roundabouts by using U.S. data from NCHRP Report 572. The model for double-lane capacity was provided primarily for critical lane (usually right-lane) capacity as a function of total circulating volume. None of the existing international capacity models separate circulating volumes by lane. This study proposes planning capacity models for two-lane and three-lane roundabouts by separate entry-lane and separate circulatory-lane traffic volumes. VISSIM microsimulation software was used first to compare with the new NCHRP models as well as with Australian (SIDRA) and German (Tanner-Wu) models. Given that predictions from VISSIM for overall capacity of one- and two-lane roundabouts are consistent with U.S. data from NCHRP Report 572, new planning capacity models were developed by using VISSIM for the left lane and right lane of double-lane roundabouts that are functions of separate circulatory-lane traffic volume. For three-lane roundabouts, planning capacity models were developed by separate entry lane (left, middle, and right lane) as functions of inner, middle, and outer circulatory-lane volumes. All variable coefficients are statistically significant, and model fits are strong.