Unsignalized Intersection Level of Service Based on Safety

Current service measures of unsignalized intersection level of service (LOS) in the Highway Capacity Manual (HCM) do not include safety measure; thus, the LOS cannot reflect intersection safety situations. In order to make the LOS of unsignalized intersections fully reflecting traffic efficiency and safety, the concept of safety level of service (SLOS) was proposed. The models for SLOS were developed, and the current LOS service measure (delay) and the studied SLOS evaluation index (risk index) were combined to form an improved service measure (delay and risk index) for unsignalized intersections. According to the original LOS criteria and distribution of risk index values of SLOS, the improved LOS criteria were defined. The application results show the improved LOS criteria can thoroughly reflect the operational and safety performance of unsignalized intersections.