Review and assessment of techniques for estimating critical gap at two-way stop-controlled intersections

Abstract

Critical gap is a vital parameter in the analysis of two-way stop-controlled (TWSC) intersections. Due to the complex traffic operations at these intersections, different researchers have proposed different techniques for its accurate estimation. This paper reviews several of these popular techniques which were used in the analysis of TWSC intersections over the past 60 years. Application procedure of each of these methods, along with their advantages and limitations are also included. Most of these methods provide the mean value of critical gap, while a few gave the entire distribution of critical gap. The accuracy of these methods is checked through simulation. Through movement at a four-legged intersection formed by two single lane one-way streets were simulated in VISSIM software and critical gap values for this movement is compared against estimated critical gap from various methods. The study found that the estimates of many of these methods are dependent on the volume of conflicting traffic. Maximum Likelihood Method is found to give the closest and consistent estimate for critical gap followed by Probability Equilibrium Method and Raff's Method.