Toward a Capacity Analysis Procedure for Nonstandard Two-Way Stop-Controlled Intersections

Two-way stop-controlled (TWSC) intersections are one of the most common forms of at-grade roadway junctions in the world. These intersections are typically located where a minor road intersects or joins a major roadway and stop signs are placed on the minor approaches. When the major roadway and the traffic that it carries go straight through the intersection, it is a standard TWSC intersection. In many places, however, the prevailing traffic and the major roadway do not continue straight through the intersection. In such cases, the major roadway bends at an angle at the intersection, and the stop signs on the minor streets are placed on adjacent legs of the intersection. These intersections are nonstandard TWSC intersections. Nonstandard TWSC intersections are found frequently in some countries and exist in most. These intersections are officially recognized in traffic codes and manuals in Europe, Australia, and the United States, yet the Highway Capacity Manual (HCM) TWSC procedure does not specifically handle these intersections. In fact, a literature review yielded no established procedure for the calculation of capacity at nonstandard TWSC intersections that would consider the specificities related to the layout of the approaching roadways and the characteristics of the traffic flow, such as the critical headway and the follow-up headway. This paper demonstrates the uniqueness of nonstandard TWSC intersections, reports analysis results from field data collected at several similar nonstandard TWSC T-intersections, identifies discrepancy in critical headway figures and level-of-service ratings that can result from the use of the HCM procedure for TWSC intersections, and calls for further research on the subject in other locales.