A Two-Step Microscopic Traffic Safety Evaluation Model of Reserved-Lane Facilities: A Highway Bus on Shoulder Case Study

When traffic operations of reserved-lane facilities are not appropriately accounted for, there is a potential for the occurrence of traffic safety issues. One problem that typically has to be addressed is related to increasing traffic interactions within merging/weaving section. That is, depending on the geometric alignment, the users of reserved lanes may be exposed to an increased number of conflicts with the vehicles on the adjacent lanes due to merging/diverging and crossing maneuvers. In this study, a two-step microscopic safety evaluation methodology was applied to a Bus-on-Shoulder (BoS) facility. This method uses vehicular interactions generated from VISSIM and into the Surrogate Safety Assessment Model (SSAM). In order to improve operation and safety performance, this study investigated different access management solutions to existing geometric alignment. Another contribution of this study is the introduction of a new conflict classification and calibration method using a binary matrix principle. The proposed method provides a more accurate estimation of conflicts classification using the existing SSAM software. Real-world traffic data was collected and used to calibrate a traffic simulation and safety analysis model of the study area. The analysis procedure used in this study is generally independent of the type of geometric alignment so that it can be deployed to other similar reserved-lane facilities. The results show that traffic operations along the corridor can be significantly improved if the geometric alignment limits interaction opportunities between vehicles on adjacent lanes. The case study tested showed that a 50-meter yield-merging section at the end of the BoS segment reduces significantly the interactions between vehicles in the adjacent lanes.