Estimation of critical gap of U-turns at uncontrolled median openings

Abstract

The estimation of critical gap is an important traffic parameter and this is useful to estimate the capacity of U-turning vehicles at uncontrolled median openings. In this study critical gap is estimated by four different methods by collecting data at seven median openings in India. During field study it was observed that, the heterogeneous traffic in India operates very peculiarly and the rule of priority is often violated and aggressive behavior of the minor stream vehicles compels the major stream vehicles to slow down to provide sufficient gap for the U-turn maneuver. These peculiar characteristics warrant for a re-look into the methodology of critical gap estimation. An unconventional method of critical gap estimation using the merging time of the U-turning vehicle is proposed. The merging time to clear the conflict area at uncontrolled median opening was calculated from field data and this time is utilized to estimate the critical gap for different categories of vehicle.