CAPACITY ANALYSIS ON MULTI-LANE ROUNDABOUTS: AN EVALUATION WITH HIGHWAY CAPACITY MANUAL 2010 CAPACITY MODEL

In this study, capacity estimations with the incorporation of highway capacity manual (hcm) 2010 method are evaluated. parameter based sensitivity analysis on calculations with the new hcm formula and a comparative evaluation of the new methodology with two most common capacity analysis methods, i.e., the method of critical gap acceptance and the method of regression analysis, are performed. maximum and minimum headway intervals of follow up time and critical gap parameters are alternated within the sensitivity analysis. the transport research laboratory formula for regression and australian formula for gap acceptance method are considered in comparison. relative comparisons of predictions on capacity by hcm2010 method, regression analysis and gap acceptance method are presented considering field data obtained by observations at two roundabouts in izmir, turkey. the results of the study show that the hcm2010 formula led to lower capacity estimates than regression analysis and higher estimates than the gap acceptance method. regarding the real capacity observations under high circulating flow-rates the hcm2010 method yielded to more appropriate results than the regression method. in addition to comparisons, studies on the sensitivity analysis show that entry capacity estimates possess sharper changes as smaller follow up headways are accepted.