Critical Gap of Two-Wheeler in Heterogeneous Traffic: Comparing Occupancy-time Method and Raff's Method

The critical gap is the most important concept in the analysis of unsignalized intersections. Two-wheeler is the primary mode in India, constituting almost 75% of the vehicle population. The Occupancy-time method is one of the few methods suitable for critical gap estimation of modes other than automobile and in heterogeneous traffic. The present study aims to check if the Occupancy-time method is indeed a better estimator than the existing methods for two-wheelers in heterogeneous traffic. The gap-acceptance data and volume data are collected from five unsignalized intersections. The approach-wise and overall critical gap is estimated for the through stream, right stream, and also combined stream using three methods: Indo-HCM empirical method, Occupancy-time method and Raff's method. The estimation results and subsequent %error show that though both methods satisfy the consistency criterion, the Occupancy-time method estimates the critical gap more accurately than the Raff's method. The Occupancy-time method accounts for the proportion of heavy vehicles and traffic heterogeneity, while the Raff's method does not. The study thus finds that the Occupancy-time method is a better choice than the Raff's method for the critical gap estimation of two-wheelers in heterogeneous traffic.