Estimation of critical gap of U-turns at uncontrolled median openings considering Iran’s driver behavior

Abstract

ABSTRACT The critical gap is typically used to determine the capacity at unsignalized intersections. A few studies have been carried out on the estimation of the U-turn critical gap at uncontrolled median openings. In this research, the critical gap was calculated using four well-known methods, Maximum Likelihood Method (MLM), Ashworth’s, Raff, and acceptance curve for different types of U-turn vehicles at four uncontrolled median openings in Iran. The data were collected using video recording. The results showed that MLM is the best method for calculating the critical gap according to the conditions of Iran. According to this method, the average critical gap was obtained 3.23 seconds, which was very low compared to other countries. Moreover, the result of MLM showed that the critical gap for Heavy Vehicles (HVs) drivers was almost less than car drivers, indicating the behavior of HVs drivers was more aggressive.