Level-of-Safety Service for Safety Performance Evaluation of Highway Intersections

Safety evaluation for highway safety performance is generally based on traffic crash analysis or traffic conflict analysis. However, in China, it is quite difficult and time-consuming to obtain historical crash data or traffic conflict data, mainly due to the lack of routine procedures and strict requirements for traffic data management. A research project was performed to develop a procedure for highway intersection safety performance evaluation with limited requirements for field crash and traffic data. The concept of level-of-safety service was introduced, and corresponding models were developed. Variables included in the models for level-of-safety service were intersection geometrics, traffic conditions, and roadway and environmental conditions. Conceptually, evaluation models under ideal conditions are based only on intersection conflict points (not number of conflicts) between motorized traffic, motorized traffic and nonmotorized traffic, and motorized traffic and pedestrians. Variables related to geometrics and traffic control conditions under prevailing conditions were used to adjust the level-of-safety service under ideal conditions so that level-of-safety service under prevailing conditions could be obtained. Field data were collected and a questionnaire survey was conducted to obtain model parameters, and expert panel field evaluations were performed to validate performance of these models. Similar to traffic level of service, six levels (A to F) were used to evaluate intersection safety performance, with Level A indicating the best safety service and Level F indicating failure of safety performance of the intersection.