Determination of the Critical Gap Acceptance and Its Associated Level of Service in an Uncontrolled T-Intersection: A Case Study

Unsignilized intersections could be divided into three main categories, namely uncontrolled, controlled with yield signs, and controlled with stop signs. High dependency on drivers’ behavior, traffic characteristics, environmental conditions, road geometry, etc. makes the operation of unsignilized intersections to be one of the most sophisticated amongst all other types. Driver’s critical gap acceptance plays a key role in the estimation of level of service in aforementioned intersections. Gap acceptance is a time interval in which vehicles in lower priority would consider an available gap in higher priority appropriate to make a safe and perfect maneuver. Driver’s characteristic like gender and age, traffic volume conditions, acceleration capability of awaiting vehicles in lower priorities, and speed of vehicles in higher priority can dramatically affect the performance of intersection. There has been a great effort to figure out a connection between critical gap acceptance and its effective parameters to come up with a comprehensive model. In this manner, three simple methods, to be specific, Average Accepted Gap Method, Cumulative Acceptance Method, and Raff Method, have been utilized to analyze gap acceptance time data and conclude with a single representative number. The resulted critical gap acceptance time is then applied to Highway Capacity Manual (HCM) formulas in order to run several analysis regarding the sensitivity of level of service on different factors.