An evaluation of supplemental signing at two-way stop-controlled intersections

Abstract

Drivers entering a two-way stop-controlled (TWSC) intersection with similar approach geometries and volumes may make the incorrect assumption that all approach legs are required to stop at the intersection. To respond to this safety concern, traffic engineers developed supplemental signs to remind drivers on the stop-controlled roadway that vehicles on the major roadway are not required to stop. The signs are generally placed directly underneath the STOP sign with a typical legend "CROSS TRAFFIC DOES NOT STOP." The objective of this thesis was to investigate the effectiveness of these signs in reducing conflicts and accidents at TWSC intersections. Traffic conflict and accident data were obtained for six TWSC intersections in Texas; three locations where supplemental signs had been installed and three locations with only a standard STOP sign. Only cross traffic conflicts/accidents were analyzed. A cross traffic accident/conflict was defined as an incident involving a vehicle on the stopped approach and a vehicle on the through approach. Conflict data were collected with a video camera mounted on 9.1 meter telescoping mast, Accident and conflicts were not significantly different where supplemental signs have been installed. Probability distributions were developed to establish 90 percentile levels for both accidents and conflicts at TWSC intersections with 5,000 to I 0,000 total entering vehicles per day. These values were found to be 18 conflicts per day and a mean accident frequency of five per year. The relationship between conflict and accident frequency was determined to be a positive linear relationship. The recommendations provide guidelines for future evaluations of safety at TWSC intersections.