Critical gap is an engineering concept generally used for determination of capacity of individual movements at unsignalised intersections. Majority of studies on critical gap estimation are reported from homogeneous traffic conditions where lane discipline and the rule of priority are truly respected. Vehicular interactions and drivers' behavior at unsignalised intersections under mixed traffic are very complex. In this study critical gap is estimated by some of the existing methods like lag, Harder, logit, probit, modified Raff and Hewitt methods, at two T-intersections located in the southern part of India. The results show that values of critical gap estimated are as low as 1.60 s and there is a significant variation (12%-38%) among the values estimated by different methods. This highlights the incapability of the existing methods to address the mixed traffic conditions. An alternate procedure of estimation of critical gap making use of clearing behavior of vehicles in conjunction with gap acceptance data is proposed. Incorporating clearing time aspect gives more realistic estimation of critical gap and helps in accurately estimating the entry capacity.

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