Effect of two-stage crossing of right-turning vehicles on capacity of urban uncontrolled intersections under mixed traffic conditions

Abstract

Occupancy time is a microscopic traffic stream parameter used for evaluating the service performance of uncontrolled or unsignalized intersections. Several studies have conducted in the past used occupancy time concept to estimate critical gaps considering single-stage crossing. However, various roadway and traffic characteristics influence the right-turning vehicles and allow them to wait at the median. The present study demonstrates a procedure to examine the critical gap behavior of minor road vehicles turning right from the approaches of uncontrolled intersections. The study analyzes the occupancy time of vehicles by developing frequency distribution profiles considering single-stage and two-stage crossings. Field data for the study was collected for eight hours at six different uncontrolled T-intersections in India. The analysis of occupancy time performed for each vehicle type observed in the field revealed that the ability of vehicles to turn through intersection-conflicting zone in single-stage crossing is 36% lower when compared to two-stage crossing. The distribution models fitted on occupancy time data pertaining to right-turning vehicles are varied under single-stage and two-stage crossings. The critical gap values are estimated using distribution model profiles for both stages of crossing at each intersection. Further, the movement capacity of the minor approach right turning calculated using estimated critical gap values is compared under both types of crossing stages. The percentage change in capacity is found to be significant with a small change in the percentage of two-stage crossings.