Estimation of U-Turn Capacity at Median Openings

Abstract

Median openings are provided in multilane divided roads to enable U-turns. The atypical conditions prevailing in India motivated this study for the development of a methodology for the proper computation of the capacity for U-turns at these locations. Harders’ formula has been widely used by various researchers to evaluate capacity for U-turns and this formula needs three elementary factors—namely, conflicting traffic volume, critical gap, and follow-up time. We collected the required data for capacity estimation from different uncontrolled median openings in India. We estimated the first input parameter required for Harders’ formula, conflicting traffic volume, by analyzing the lateral placement of vehicles at the median opening area. We estimated the second parameter, critical gap, by using four different critical gap estimation procedures—namely; modified Raff, maximum likelihood, macroscopic probability equilibrium, and merging behavior. The third parameter, follow-up time, was measured directly in the field. Consequently, we calculated U-turn capacity for the given traffic streams and the findings were tested against the field capacity estimated in the field using Kyte’s method. We then determined a suitable method for critical gap estimation in the Indian context by using two statistical parameters.