Calibration Factors for Safety Performance Functions

Safety Performance Functions (SPFs) are equations that estimate expected average crash frequency as a function of traffic volume and roadway characteristics (e.g., number of lanes, median type, intersection control, number of approach legs). SPFs are developed through statistical regression modeling using historical crash data and are used to enable the correction of short-term crash counts. MDOT seeks to develop local calibration factors for the Safety Performance Functions used in the Highway Safety Manual (HSM) predictive method. SPF calibration factors tailored for the local conditions and crash frequency within Mississippi will help MDOT identify high-priority locations in which taxpayer dollars will be better utilized to keep the travelling public safe. The development of these SPF calibration factors will help better automate the crash prediction process within the Safety Analysis Management System (SAMS) program used by the MDOT Traffic Engineering Division. The SPF calibration factors will help MDOT prioritize the spending of approximately $35 million in Highway Safety Improvement Program (HSIP) funds annually.